Honestly, I don't know if modern gaming hardware is up to the challenge, but you have to admit that it would be damned cool.
Historically water and foliage have been some of the hardest things to to simulate. Well, not hard per se, more that they're extremely calculation intensive.
Consider that "Squirrel Simulator" popped into my head on the way to my pharmacy a while back when a squirrel leapt, as squirrels often do, from one branch onto another. These weren't the big sturdy branches, but rather the more numerous end branches that spread from the tree like pseudo fractals and cause the branches of one tree to become mixed with the branches of another without the two ever actually touching.
Naturally the branch that the squirrel leapt from reacted to the downward force exerted by the jump followed by the sudden absence of the squirrel's mass, but the more impressive thing was on the other end of the transit. The squirrel caught it's intended branch and for a moment it and the branch dropped like a rock before a new equilibrium was reached and squirrel scampered off to preform its next feat of acrobatic daring that would make human athletes envious.
So we can imagine Squirrel Simulator where you run, jump, climb, and eventually unlock "Flying Squirrel Mode" (spoiler: they don't fly, they glide) through a world of branches and leaves and sprouts and the giant gap between the bottom branches and the ground and generally go around being awesome and having a good time.
But the amount of information would be massive, no two trees are the same, after all, and if you took shortcuts by making them that way it would show and the appeal would be lost, nor can you simply procedurally generate the trees using stochastic methods to keep them different and then discard them as soon as they're out out play. Learning the best paths and experimenting and improving would obviously be an important part of the game.
But each leaf, each shoot, each branch, and ... well actually we can get away with pretending the trunks never move outside of windstorm levels because those things are massive fuckers that are hard to budge, but everything else needs to move in a realistic way in a system that's constantly having internal effects. When one branch hits another that needs to cause a chain of reactions, the very air displacement as the squirrel launches itself through the empty space between one branch and the next is going to affect the leaves and thus the sprouts.
ANd the rendering, sweet fuck the rendering. Maybe we can simplify the behind the curtain stuff representing branches as lines with a variable for thickness, though this is certainly not ideal, but to actually put the damned thing on screen and have it not look like shit? Holy Mary mother of god and all her wacky nephews, think of the sheer polygon count.
So perhaps the world hasn't yet progressed to a point where it is ready for a game as great as Squirrel Simulator but I'm putting it out there now. The idea is in the nonexistent aether now and you can't stop it.