You can already block scenes out very effectively with the CSG nodes and objects. Unibuilder looks good with a lot more control and ease-of-use but it's not going to be a million miles away from what is already built in to Godot.
for my purposes Unibuilder looks to be millions of miles better than godot's built in csg workflow. i've done it over and over in many projects and it's such a pain
btw im not the one who disliked your comment, i realize unibuilder might be more than what some people need, but MOST people will want what unibuilder has to offer compared to godots csg.