Well, while I'm not planning on actually making a few things, I do have a some ideas bouncing around in my head- though nothing concrete to actually make a proper game with, probably. So I guess I can share one from the top of my head.
Y'know, playing skyrim, and having the devs boast it's organic open gameplay, I've always thought to myself that there's a better to way to go around this. Not like this is going to solve that problem of shallowness I find whenever I play that game, but I feel like this is a principle that they should pursue if they really want to create a proper "create your own story" fantasy.
The story, first of all- should be non-linear. That's the one thing western devs can't seem to wrap their head around.(imma lookin' at you, BioWare, Telltale) Everyone seems to think that a karma system's the way to go but the fact is it should work in the side instead, having flags as a main mechanic(I'll get to it later, this is just rambling so it's not really organized).
Essentially, instead of one straight-line slog of a main story or whatever what should be done is that the whole thing is fragmented short stories- with the flags the player has set up being a modifier to the situation. Don't be afraid of your game having no difficulty curve, pretty much don't scale your game towards the player's level automatically, that's the worst idea you might ever have in your entire life, instead make a work around with the lore why a certain area is so dangerous, and if the player steps in unprepared or cocky let 'em have it.
Let's say we can give an example how this sort of non linear story telling could work:
First, we have a village, let's say it's under attack by bandits. MC-kun comes along, now he's tripped the "seeing the village under seige" flag, he has a couple of options that pops in his mind to play with:
1. Help the villagers find against the threat.
2. Leave the villagers alone.
3. Find the bandit's camp and do something.
4. A butt load of other things, I suppose.
You see, whatever he does earns him a little flag to let the NPCs and other things respond to the things he's achieved. This happens with everything in the game, where the story is pretty much connect the dots in an entirely different way than environmental story telling.
But, seeing that this is a non-linear story, what if MC-kun never even reached the village? Maybe he reached the bandit's camp first, or maybe he wasn't even anywhere near the happenings- well, that's just fine. Not showing everything for the player is a good indicator of replayability, one of the best things to work with your game if you're planning for it to be open.
But now we also have another problem: "Gosh darn, there's so many choices, this is going to take so long to make!" The answer is easy for that, don't be afraid to make it short. If you're afraid people will complain about starting over again, and again, add a new game+ mechanic, or a time travel mechanic- maybe even make levelling up a butt load easier than what it normally would be(after all player empowerment can be achieved without ruining scale and balance).
With that, here's a nice little example idea. Think typical elder scrolls' mechanics, but with a story in the same format as this instead of their Main Story+Side quests kind of trekking. Like, maybe you're a hero, showing up to stop an evil from invading a certain kingdom within 6 days, or something. Maybe you can to the different groups of folks an appeal to them to fight by your side, or you can be some sort lone BAMF that's just going to spend all his time training to take the evil army single-handedly. iirc Skyrim's days last for about an hour or so, then add events running in parallel that only appear in a specific date, then increase the xp rate by 50%(woah) and I think it would be a very enjoyable RPG that you could pick up and play anytime.