So, I watched this video and it brings also a definition at the beginning (of a long and interesting journey throught RPG-history). In the definitions it mentions the things we in the thread and I in my attempt mentioned, but one more, and I could smack myself for not getting it: world building. Sure, not every RPG has good world building, but so has not every RPG deep statistical mechanics or a deep story. But if I think of RPGs, many of them have detailed worlds and that is a thing many non-RPGs actually lack.

So if you're interested, here is the video:

https://www.youtube.com/watch?v=8o3i10OuMFQ

It's always fun to watch NeverKnowsBest's essays *though they can be really long at times).

As for world building - yeah, prior to Hickman Manifesto, that was the main focus, playing in the world built by your DM, with stories that emerge from those gameplay sessions. As Tolkien himself said, "I wisely started with the map". It is around '83 and Hickman's Castle Ravenloft (though you could see beginnings of it in their previous module, Pharaoh) that "story first" approach began to (unfortutanely) dominate D&D.

From the creator of Fallout:

Is the option for a non-linear path a hallmark?

Pretty much. But depends on who you ask.

VRPGs started as an attempt to convert TTRPGs to computers. One of the defining things in TTRPGs is playing the world in which you can try anything - which doesn't mean it will succeed - but you can try it. That is actual non-linearity, not the open world part. That automatically breaks any fixed structure, which means that, if your DM/GM is not some "failed novelist" who pushes you down "my way, or highway" railroad track, your story can take quite a bit of turns.

That said, that's extremely hard to do in VRPGs...nigh impossible actually, given that you can't code everything players can come up with - AKA, there is no DM/GM to improvise on the fly, and to pull strings behind the curtains. Sure, you can make world that is fully system based and drop players into it and let them do whatever they want to do, and that would actually be much more similar to how TTRPG began, where DM/GM is more of a impartial referee that "runs the world", but games that are trying that (like Kenshi to a degree, which is great game for what it does) tend to suffer from that same lack of actual DM/GM.

In early 80s, TSR, company behind D&D, started to push for that prewritten linear story driven approach with Dragonlance (they could sell more books that way)...I'm not sure how much certain VRPG designers from that era were influenced by it, but subsequently there is definitely a lot of RPGs that are made like that. Which makes sense from budget perspective, given it's way, way easier to make such game. Luckily, there where designers that kept to original ideas of playing the world, instead of playing the story, so there's plenty of games that tried non-linearity (with various degrees of success).

With recent advancement in AI NPCs (Ubisoft's prototype of AI NPC is a great example of what is to come), AI procedurally generated imagery and even early attempts at making fully-fledged AI DMs, I don't think we'll wait for too long to actually see the first VRPG that actually gives (to some extent) freedoms of TTRPGs.

Well, after wondering for a longest time why nobody ever implemented something like Sims AI into an actual RPG, there seem to finally be games, albeit from smaller devs (as it's common) that are trying to do something like that.

City 20, as I understood it, is survival RPG where NPCs are unscripted and instead have their own goals and motivations which governs them, which translates to interactions and reactions to player as well. It looks fairly janky all around, and I don't think game itself will be stellar, but givent that it takes (as per devs) inspiration from Dwarf Fortress and Rimworld, I'm really looking forward to see how far it pushes "AI" NPCs.