I think Korra is just going to have the four books. I hope that they'll continue her story, and if not that, then a new Avatar's at some point.
Still no Flurry of Blows replacement that I can think of. Maybe something that let's them use a standard action to make an additional attack at half-BAB?
You should probably consider only adding things that differ from the monk it should narrow it down from 38 pages which is a bit much for any class