The only thing that keeps me even a little optimistic is that why wait so long to release them if they're just going to be half ass glorified missions?
This, I'm thinking they WERE, then R* realised that they'd need to pull more then a rabbit out the hat.. So went back to the drawing board!
If they end up being just like that leaked heist R* will be needing a next gen/gta 6 announce pretty soon after, otherwise they'll lose the masses.
Im personally looking more forward to a mission creator, i think that will give Online a new lease of life! For heists to do that for me, they need to also introduce some form of class system and have the heists play on that.