I would absolutely get this if it worked w/ the PS3. I guess Harmonix doesn't like PS3 owners $$?
No, it's not financially viable for PDP (the makers of the Stage Kit)... here's the economics for you:
Of the Xbox 360 Rock Band owners (of which there are way more than PS3 Rock Band owners), there still weren't enough interested in the Stage Kit to support it at its initial $100 price point. Even at $50, it was not selling well.
So, why is there no PS3 Stage Kit?
Well, there might have been plans... after all, RB1 songs have Stage Kit support and the Kit was not released until Rock Band 2 had been out for some time, so clearly this accessory was planned since the beginning. That said, it is likely that PS3 songs (at least the first bunches of batches) had the Stage Kit light show coding included with them. However, once the sell through numbers (360 vs. PS3) started to take shape, it's clear that offering the Stage Kit to PS3 owners is even less financially viable than offering it to 360 players.
It works like this.... lets assume that 5% of Rock Band owners would be interested in the Stage Kit (which is probably way higher than is expected... I'd venture the actual expectations were way less than 1%.) For the 360, RB1/RB2 has sold 3.55 million copies, which PS3 RB1/RB2 has seen 1.54 million copies sold.
360 would have sold 177,500 units at $100, equaling 17.75 million in revenue
PS3 would have sold 77,000 units at $100, equaling 7.7 million in revenue
But, as I've said before, 5% is a ridiculous number, as would be 1%. So, take into the fact R&D, licensing, paying someone to program the light shows for every DLC song (yes, this is a continuing cost), plus the manufacturing of the unit... it only makes sense to go with the system that will guarantee the best return on investment.
I mean, just look how warily Harmonix supported the Wii with RB1 to begin with, essentially releasing the PS2 version only after the Wii had proven to be a true contender (as far as market share).