I have a lot to say about your position on "railroading", "meaningful decisions", and likely "agency" issues at the heart of your theories. I think before I try to respond though, I'll try to get your take on the below Cortex Plus's MHRP advice on Framing Action Scenes and Presenting the Challenge. I'd like to see where you come out on this. This system is as close to my table agenda and the way I run games as possible so I think its very helpful for clarity.
I don't have huge issue with the section you quoted. I think I'm going to have even bigger issues with MHRP's take on resolution. But I do have one particular issue, and it is probably where you expect it to be.
...the Watcher asks you, "How did you agree to this position?"
One of the obvious answers is, "I didn't. You assumed agreement for me." It seems to me that prior to asking how I got into this position, it might be worth it to ask whether the player does agree to be in this position. Generally speaking, with a railroad technique like 'the handwave', it's IMO incumbant not just on the player to obtain permission from the rest of the table, but on the DM to obtain permission from the rest of the table. "Would you allow me to handwave all the events between your current scene and the next scene where something dramatic happens?" And if that presumed sequence of events involves a direction of player action, then you need either agreement or stated intention. If a player states the intention, "I begin climbing the mountain.", then the DM must say, "For someone of your skills, the mountain is a mere ordinary challenge. Do you intend to climb to the top?", because the DM needs permission to jump to the summit. Of course, often the intention to engage in continious action is explicitly stated, "I climb to the top of the mountain." This too though needs to be handled carefully, jumping to the first bit of 'unforeseen' difficulty, "About 2/3rds up the way becomes treacherous, you'll need to make a difficult climb check to continue. Higher up the fall becomes increasingly exposed." The player then gets the oppurtunity to ask questions and make a decision. In general, I don't feel that a GM should ever be making assumptions about player activity that can have any bearing on the game.
The biggest problem with these sorts of scene frames is if they become reutine, the players will just sit back in the train car and enjoy the ride until they get to the next stop. There is a tendency to replace player proactive choices with DM proactive choices and put the players entirely in a reactive role. Your entire narrative of play felt to me entirely of DM proactivity (making choices for the players to get them what they wanted or what you thought they wanted), and player reactivity (responding to scenes as they were presented to them).
But I have possibly an even bigger problem with your description of play that doesn't have to do with how you frame scenes but how you resolve action. The players had no way of prediciting what the results of their actions would be, whether success or failure. There are almost comicly large and unpredictable consequences to success or failure. A failed ride check leads to a ravine appearing in the universe. A failed spot check led to the ground opening them up and swallowing them. So far as I can tell, you didn't let the players set the stakes. The players didn't express what would happen on success or failure, only their proposition. You ran this as a skill challenge, but 'on failure' neither you nor the players knew what would happen until you improvised it. Indeed, since the universe is morphic, 'on success' wouldn't have necessarily led to anything predictable either. So these desicions aren't really meaningful. It might be a fun ride on a roller coaster, but the players are on rails.
I feel you are applying narrative techniques in a situation where the players aren't narratively empowered. The result is that the players are almost entirely powerless.
Not surprisingly, I disagree with pemerton at least a little. He's right that GM force in resolution - the fact you hold and set all the stakes - leads to a railroad, but I think he's entirely wrong that GM force in framing isn't railroading. Indeed, GM force in framing is most of the technique, and the more powerful bit of the technique because its the easiest to get away with. The players are eventually going to realize GM force in resolution, and decide whether to rebel or go along for the ride. But with GM force in framing, you can railroad your players just about anywhere if you are subtle about it and they'll never know. This is especially true if you do what I call 'stage magic' where you lift the curtain occasionally to prove you are playing fair and build up trust that you are always playing fair, "See these handcuffs are solid. Test them. And look no wires.", and then when the curtain goes back down you are free to play your trick deftly. That being said, just because I know how to railroad well doesn't mean that I believe it artful DMing to do so often.
pemerton asserts you aren't using GM force in resolution, but again I disagree. Making your fortune roll in the open is hardly the be all end all of proving you aren't using GM force in resolution. Indeed, it's a form of 'stage magic'. I often theaterically roll in the open on major events, even telling the player what the stakes are: "If the d4 comes up a four, you die. Otherwise you live." But suppose I rolled in the open but didn't tell the player the stakes? Well, then it really wouldn't matter what I rolled because the roll itself was meaningless. The player could attach no particular outcome to the fortune. The contest was meaningless. The die could come up whatever and the player would still need to go, "Ok, what does that mean?" You are in that situation. The players may roll however many skill checks that they like, but its all meaningless because they never really know what is going to happen anyway. They only know that things are going to turn up in some abstract way 'good' or 'bad', although since both 'good' and 'bad' just lead to more DM framed scenes its questionable whether that has any real meaning. The dressing of the open world rooms might have changed a bit, but the basic action of play would have remained unchanged.
pemerton IMO continues to use a bunch of terms from narrative art to describe loose simulationist play. For example, he calls it shared "narration of color" that a gorge appeared as a result of unlucky dice while the PC's escape on horseback. "Escaping on horseback" isn't narration of color, but of player proposition. The appearance of the gorge would have only been shared narration of color if you had allowed the players to decide what the consequences of their skill failure had been and they had described the gorge appearing in their path and trapping them. He also inadventently brings up another problem I have with the resolution, and that's that it's pretty much entirely luck. Player decisions aren't just meaningless because they don't know and can't control the stakes, but they are meaningless because creative decisions don't determine how quickly or well the challenge is overcome since they are locked into the "skill challenge" format that forces them to overcome a certain number of arbitrary tests. And, there is probably liberal application of GM force in resolution in both your games to mitigate that problem.
It occurs to me that on some level the sort of 'surprise' we've mostly focused on in this thread might not be possible in games like this. Can the players ever 'mechanically' surprise a DM using these techniques? I can see that they might narratively surprise the DM, going in an an unexpected direction. But it doesn't seem to me like they have reliable packets of narrative force as in traditional D&D.
It's pretty much the opposite approach from the "Use Rope" skill check approach to centipede-riding that @Hussar has objected to upthread.
I'm leary of the word 'opposite' here, but it is definately different. The player knows the stakes - either I will or won't be tied to the Centipede - he knows the risk, the difficulty and the time involved in resolving the proposition. He knows that he's isn't acruing failures or succcesses leading to some surprising and unpredictable result. He can see his environment and plan for it. He knows that he is in control of his character and that the scene isn't going to evolve except as a logical consequence of something preexisting in the environment and reasonable for the environment.