Nest isn't an insurmountable issue for Revan teams, but then again nothing is as he's the most blatant P2W thing we've seen to date. As another Revan user, she's annoying, particularly under zMaul, exactly because you have to wait for her to take a turn and generally don't want to use any specials on her. I've lost to her on defense in a Q'ira / Hoda / Nest comp (the other two are largely irrelevant - I have a clever PO mate) with her being modded for protection and extra-high tenacity. It's a gimmick and not 100%, but it can work.
Juhani doesn't seem to add much to the Revan comp in place of either GK or Bastila (the only two you would consider replacing). She might be meant for additional options under a Carth Onasi lead, or to provide a generic tank for other Jedi teams. The additional speed bump from her OR tag might help tip the scales in a mirror, but that's about all I could see, and losing the foresight from GK shouldn't be underrated.
To @Woodroward 's comment on Revan not needing offense, I would assume he has never played a Revan mirror match where offense (and who gets battle meditation or retribution when) is one of, if not the most important consideration. Nothing like beating the opponent team senseless for five straight minutes to end up in a five-five tie with everybody with mostly full protection and a full menu of buffs.