I would rather there be more PS2 releases. I don't have a PS3, and don't plan to get one for a few years, when/if they get the hardware working right/decent backwards compatibility/non-ridiculous price.
That said, if I were king of the world and could make the perfect PS3 mix, it would have two modes:
One, regular game. Pop in the disc and play as you do with every other DDR game.
Two, shell mode. Pop in the disc, then select the shell mode (perhaps there's a better term?) and swap out with another DDR game disc that contains song data. A PS2 or PS1 disc - heck, while I'm wishing for impossibilities, Xbox discs too! And homemade discs with Stepmania-style vustoms songs! Point is, you'd pop in one of those discs and play it in the PS3 shell, with the same interface, grading system, high FPS, speed mods, et cetera. This would allow me to play songs I have on games with interfaces I just can't work with, such as the Xbox's low FPS and the PS1's lack of speed mods, and I could also play perfectly good PS2 games without having to have two systems hooked up to my TV.
Song packs are also a good idea, but I don't have the connection to get 'em, soI won't wish for what I couldn't use.
People dance without arrows?