For a heavy narrative system, as others have pointed out, you should go with a different system. You could still use the D&D lore, but maybe use Fate, Genesys or Dungeon World, unless you want to design a whole new game, but it won't be D&D, anymore than Fate.
As for having adventures match the pace of a novel of movie, it's not going to work. Many years ago, I played in a Buffy game. The GM wrote awesome adventures for us, which really felt like Buffy episides. It usually took us about 3 hours to complete an "episode." Picturing one of these sessions done in 50 minutes or so, and it would not have worked at all. Way too rushed.
I believe rpgs are an awesome way to tell stories, but they are their own medium, just like there are differences between novels, comics, plays, tv and movies. Don't lose sight of the strengths of rpgs in your desire to tell stories that you love from novels.
Oh, get what you are doing, I totally get it. What you don't get is you are removing player agency or the importance of such agency. You give 4 outcomes for the entire adventure (or even 40 is an incredibly small number compared to LMoP as is). That is not of interest to me.
You are increasing story telling where the DM narrates (or just reads) a bunch more than you see in your games. The lack of story/narration at your table is due to your table, not the system. You can easily player D&D as is where each player narrates everything they do.
Agency is important. It is so important as to be required for the "D&D Experience" imo. For example, one of my parties when they did LMoP and Cragmaw, they simple overran the dang castle, the didn't engage the guards, instead they flooded into and through like a tide. The dropped a darkness in the foyer and all the guards proceeded to wait and then progress into the darkness slowly. By the time all the guards figured out what was going on in the foyer, the party was already fighting the BBEG at the end. That is still a story and a tactic they discuss 2 years later when assaulting other strongholds.
And, if you tell me your ND&D could make that one of the options, then you just don't get it. Player agency is not about any one event, decision, or outcome. It is the players making decisions for their characters that are foolish, uninformed, and/or brilliant. These decisions, and the results as narrated by a good DM, are what makes memories. Go read online the stories that people tell of D&D from 30 years ago. They are not about what was scripted, but about what happened due to player agency.
As for published adventures being sort of railroady... sure, most of them are written that way because they need to be accessible to DMs that don't know better. A DM that chooses to can allow an adventure to go in any direction, and just because an encounter is not in the published adventure, is a poor excuse for a DM to not allow an encounter (or any other type of event) to occur.
Another thought, if you want an adventure to be over quicker, then you are probably missing out. Their is value in the journey. Just like life and relationships, the journey, what happens between where you start and the end, is often more important, and almost always more memorable, that getting to the end.
Okay. Now I feel heard. Thank you Arilyn, LordE, and to the others who responded. And to Bobble and LordE for the laughs. (What's wrong with Kindergarten Storytime: The RPG? haha)
I admit I hadn't thought it all through from start. And even my own parameters have continued to shift. I do believe a very fun game could be made along the lines I'm envisioning. And that even with a "novellic" or "cinematic" system, a sweet spot could be reached which made space for a resourceful DM to improvise in response to player agency.
My initial post was fueled by four legitimate desires:
1)
For the battles to be a lot quicker, yet still satisfying. And for stories/adventures to be completed in one or two sessions...including "bigger" novellic stories (not just a small dungeon crawl). I was struck by how long it takes (in Real Time) for us to run a battle in 5E versus how quick (and satisfying) the battle scenes pass in the Icewind Dale novels. AFAIR, back when I DMed BECMI, the fights and adventures were significantly quicker too.
(Along these lines, posters offered good suggestions: best practices for quickening 5E fights, and also enjoying the journey. I still hold that a much quicker system could still be satisfying, which retained full player agency. Even if it be The Black Hack. Or Mike Mearl's alleged "one-roll-per-encounter system.")
2)
For all the "picturesque" moves which characters do in the novels to be fully supported by the game-system itself. Given the honed storytelling work when went into writing the novels, a lot of this stuff is an iconic expression of "D&D-ness", even though its not really supported by the rules.For example, the scene where the Companions of the Hall battle a horde of trolls, and the fire spreads from troll to troll. That was great. Yet not really supported by the Rule-As-Written (in any edition). To be specific: the D&D troll stats ought to have Fire Vulnerability, and once lit also take persistent fire damage, and also have some sort of "Troll Pack Conflagration" weakness: like, if a flaming Troll is adjacent to another Troll, the other Troll has to make a DC20 Dexterity save or be ignited, and so on. I could probably give dozens of examples from every D&D novel where the characters do awesome, picturesque things which aren't really supported by the game. It's not just a matter of having a better DM who's adept at imaginative descriptions of damage dealt. And it's also not just a matter of novel authors being too "loose" with the rules; but rather, the novels have "bested" the game on which it they were based, and raised it to a higher degree of storytelling fun...this "leading edge" ought to work back on the game itself.
(Along these lines, people suggested more "narrative", "degrees of failure/success" or "descriptive move" based systems: Feng Shui, Dungeon World, FATE, or Genysys system. I'd also add Cortex/Smallville "relationship RPG". But in any case, I'd want it to be fully immersed in the D&D Multiverse.)
3)
For the picturesque descriptions of places and landscapes from the D&D novels to be included in the TRPG modules. For example, just last night, I read in the Halfling's Gem novel that Drizzt and Wulfgar visited Coneyberry and Agatha the Banshee. Which my players have recently visited in the Starter Set. Not being a FR expert, it would've been great for the Starter Set to include, say, a DC10 History check for the Coneyberry hex, which revealed a summary of that story (I guess it was over a hundred years ago), and which even pointed the DM to the novel for a more fuller description, as a flashback.
4)
For someone to do groundwork research in breaking-down exactly what "Actions" are happening in the hundreds of D&D novels. And then to reverse engineer all that cool stuff back into the game...whether that be via new options in 5E, or via a new "novellic" system. Yeah, I know WotC team doesn't have the manpower to do such a project nowadays.
Well, I said my piece. Thanks again for the good ideas and laughs!