Just as an aside question: in a DM-driven game the DM can now and then introduce non-genre-convention stuff into the game e.g. a spaceship into a sword-and-sorcery setting. How could this be done (if at all) in story-now where the players can't declare out of genre and the DM has to stick with what the players are doing?
Wow, talk about 'bug vs feature.' Yes, D&D was a child of the 70s, with all the grace and dignity that implies. There's nothing in the rules of D&D per se, that 'allows' (or prevents) the DM from dropping a spaceship into what had otherwise been a very poorly-emulated High-Fantasy/S&S-sub-genre FRPG - indeed, Temple of the Frog did exactly that, nor was it alone.
If there's a table convention that you actually stick to one genre, that genre can be High Fantasy or S&S or Planetary Romance, or goofy Science-Fantasy. You just have to own up to it earlier. You can't bait-and switch, offering Tolkienesque High Fantasy and then delivering Sid&Marty-Kroft-esque science-fantasy.
That - and the reverse, for example doing story-now in 1e D&D - is only true if you take the view that the game/campaign/style of play is subservient to the system rather than the system being subservient to the game. It's always possible to make something work given enough kitbashing of the rules - it just sometimes takes more effort than it's really worth.
Whether your drop one system and try a new one, or extensive modify a system to make it work for your game/campaign/style of play, you're not 'making the system subservient to the game,' you're changing to a different system. By the same token, when you pick a system that works up-front, for the game/campaign/style of play you want, that's not making your style 'subservient to the system,' it's just doing some legwork to find a system that's a good fit, instead of a lot of design work to 'fix' a system to make it fit.
This is in fact one of my own pet peeves and always has been, when people use these terms interchangeably. It's annoying at the least, and adds greatly to confusion at the wosrt.
I'm surprised, because I'd expect you to be over on the immersion/first-person end of the spectrum.
But, yes, it bothers some and seem meaningless to others. Obviously if you say a character chooses a feat or a PC rolls the dice, you mean the player. Obviously if you say a player was turned to stone by a medusa, you mean that player's character. ;P
I can tell you, forcing Gygax's AD&D into "story now" service is not easy.
Forcing 1e AD&D into /any/ style, including Gygax's own quasi-adversarial 'skilled play' style, is not easy. It's just not an easy game no matter how you use it. It's like trying to spin circuit boards out of primordial sludge.
Trying to do dungeon crawling of the classic D&D variety would be impossible, or near enough to, using Cortex+ Heroic.
Telling a story of a dungeon crawl - the one dungeon crawl in decades of campaigns that made a good story when you retell it again & again, that is - would be quite possible, though, wouldn't it?
Of course you can introduce new rules if you want, and take out the rules that get in the way, but that doesn't show that any system can do anything; it shows that if you design the right system, it can do what you want.
Modding systems is design work, yes. I kinda don't want to admit that to myself, because I love to hide behind "I'm not a designer!"