The nesting problem for smaller screens has been addressed. I am looking into the nesting issue beyond 2 levels, I would like it to go no deeper myself.
As far as the reply box, I mentioned that it won't chage. That is the location the developers of this platform chose, and we've decided to leave it be. Implementing it as a user based option isn't feasible.
Smaller avatars and thread title sizes are possible, although I don't know that it's really a big concern. What's the problem you have specifically?