I do like the idea of a fully destructible environment.
It'd be pretty cool when clearing out a town to be able to burn down the houses too. Though having this, there would have to be a system to rebuild them as well, which would have to be done really well.
I think it'd be awesome if you could rebuild and make it a different building, make your own house! I'm not talking about on the level of Sims or anything, but being able to choose different floorplans haha. Sounds cheesy but it Would be fun and Wouldn't be a requirement for people playing so they couldn't complain.