I was thinking that it would be epic if R* added the option to plant & detonate dynamite in Free Roam.
Example: you are being chased by a massive posse, you run across a bridge or downe a small gorge etc. and quickly plant dynamite. Then when the posse comes you detonate it and blast the whole posse.
Also I was thinking that a good game mode would be that a Sasquatch/Bigfoot randomly spawns anywhere in Tall Trees in Free Roam and you have to go and hunt it but you can't see it on the map and it is hard to find, you can't lock onto it, it can take lots of bullets and easily escape etc. and the person who kills it gets 1000Xp and anybody that gets an assist gets 500Xp. When a Sasquatch spawns you get some sort of alert on screen to tell you that there is one and it can spawn anytime.
You could just imagine how fun it would be getting a big posse together to go hunting for it.
Also, I think Sasquatch would make a good Multiplayer character and it could be made the size of other characters so that there wouldn't be any tech. problems. It would add a bit of variety to the game.
If the game mode I mentioned was done there could be challenges to unlock the 3 different types of Sasquatches in the game which are the main sasquatch in the cutscene, a male sasquatch and a female sasquatch.
Anyway, what would you like to see in the future excluding trains and lasso's which we know everybody wants?...