Nice to see innovating trying to solve the common threaded comment design flaw (not a big fan of the forced vertical repositioning on stack un-/grouping as even with animations it slightly breaks your visual fixation)!

Though for the width issue there is a simpler solution for most of the cases (except for very deep trees) - just make the margin smaller.

In the product video there are two relatively big margins - left of the comment box and left of text within the box. But this is pure waste, you don't need so much whitespace to signal text hierarchy.