Amazing idea ! The visuals are very nice :) . The player will be able to modify the world, but will it be possible to create new assets (tree, chest, etc...) with mini-voxels for example ? Also something that would be cool is to use the virtual players' view, so you will experience in a first-perso view. I think some tycoon games do this (on roller coasters for example)
Also, what are the target platforms ?