Well the thing is, build mode *is* different in TS4 in some respects (unlike between TS2 and 3, I mean) .. at least the way some things are handled in game is different. What I don't know (and would appreciate insight on) is to what extent the underlying basis is different -- perhaps in a way that would make implementing this a total nightmare (and thus not feasible), even when it would be "technically not impossible".
I know I'm also guilty of calling it "removed" in my post above, but maybe it wasn't "removed" so much but rather "not implemented again" (because it would be a different feature now)? It might be difficult to handle those flexible-height walls and foundations in conjunction with cfe, for example. Or it might not be. What would happen when you have a "high" wall, shorten that very much using the cheat, and then make it a "low" wall? TS2 was capable of handling less-than-zero heights, but is TS4?