7 Days to DIe - Looks very impressive and plays pretty well there are alot of niggles in it but they will be worked out when its in full production I guess. Overall a pretty good game, have only played this briefly had a little trouble keeping my attention focused on it tbh.
Starforge - Having owned this since the Alpha was released I have to say this game will be amazing once they get it to the standard they want... the current release is utterly behind the video (which was of the free version they used to have) This is due to them porting the whole game code into a new updated engine. There is a total competitive fighter feel to it as well but only in certain gamemodes the infinite terrain is truly beautiful to behold
Cubeworld - Amazingly haven't got around to trying this out yet but its more RPG than sandbox like Minecraft from what I see so in the topic I would have to disagree about it being a replacement.
Theres another game I would throw in for consideration
http://playstarbound.com/
Although this is more like an updated Terarria.
In short Minecraft will never be replaced in my opinion its far too niche and will always be hailed as the most popular and well known in the voxel sandbox genre
Also even now its still a massively entertaining game given its current age.