That's sort of the purpose, if I'm in RC's head enough to grasp where he's going with this. If you can actually field an army of divas, then yes, their combined might would be extremely potent. However, I submit that they tend to move a lot, and they must be within 30' of each other at all times; that's only six squares on a battle grid, so there's a definate limit to how far it'll take you. CAN it be exploited? Sure.
Have you ever tried herding Divas? I'm just saying, it ain't the easiest.

You think tossing two DMs in a room to discuss campaign structures gets ugly? You've never seen artistes go toe-to-toe. I'm not saying you don't have a point, I'm saying that if you were to get that many Shadowfists gathered up in one spot, it would be pretty rare, and the effect would be understandably spectacular.
Considering, though, that they don't get this until 3rd, would you consider capping the bonus at level, RC? i.e., "You may gain the bonus from a number of Dancing Partners up to your level", which wouldn't completely prevent abuse, but 15, 15th level Shadow Dancers would be a sight to see. Shoot. How to win a bar room brawl, in eight easy steps.
Where was I?
- Plie, Floorcraft & Evasion all stack with Dances. Excellent.
- You added Locking Step!
COOL!
- I'm grepping your feat structure better; clearly this is an extensive rewrite. This looks much more polished, though.
- Am I assuming the Monk unarmed damage table, as well as the size chart?
I can think of all sorts of variants for this, but I don't want to deluge you and have you sitting there half a day going, "No... nope... nah... eh!... no, no nevermind..." So I'll quit while I'm ahead.

I have no further comments at this time. Sounds much more ominous when I say "At this time," don't you think?
"You were just going to turn my statement into a question, weren't you?"
"Ah... no, no... well, maybe."