Let’s say that Kanai Cube has 1 weapon slot, 1 armor slot, 1 accessory slot, and 3 free for all slots.
Will this improve the build diversity of the character or everyone will eventually end up using the same setup for their character (for e.g. 1 DPS, 1 DPS, 1 DEF, 1 DPS, 1 DPS, and 1 DPS for Kanai cube setup)?
You can add as many slot as you want, there will always be something on top. Look at the current season with the 4th cube slot: meta builds may have changed slightly but at the end of the day, the best build is still better than the second best build.
No, it will not. This is a poor idea in my opinion and not very well thought through.
It certainly will not. Even the 4th slot we currently have as a theme barely changes a thing. The most visible change would be power creep since players would only add damage modifiers to those free slots.
Power creep and server lag. You’re welcome. It ain’t gonna promote a wacky build when you can have emphasize your profession and increase efficiency on the yard stick you’re planning to run.
Good question, I think that most would try to maximize the damage for their build and as that was done with they might consider boosting another skill or most likely try to increase the defence.
No it wouldn’t help make more diverse builds, but Kanai’s is a cube with six sides, so it would make sense from that angle. Kanai’s Tetrahedron doesn’t quite have the same ring to it.
Kanai’s Rhombicosidodecahedron… It doesn’t even have a ring to it because I can barely pronounce it. Although, 62 cube powers at once… Hmm… 
Well of course, because builds would be different from how they were in the past. Just like they are different now. And then we all go back to having “the same old build everyone has”.
That was sarcasm of course.