I don't own a PSX, PS2, or PS3, but here are some of my thoughts on the idea (and some thoughts for improving DDR in general).
Graphically, I can't think of anything new that Konami can do that uses the PS3's capabilities (except bringing back background videos). If there is DDR on PS3 (which there probably will be), I think that Konami will use the cuts from Beatmania IIDX for any IIDX songs that appear on future DDR home versions (and arcade versions). Also, I think to see the videos from Beatmania IIDX on any songs imported from IIDX, and I think that there should be full-length videos on all of the other DDR songs (similar to Pump It Up).
As for music, they should put at least all of the music (and steps) featured on all of the PSX DDR games (and possibly all of the PS2 DDR games) on the first PS3 DDR game that comes out. Seeing all of the songs from the early arcade mixes (1st Mix, 2nd Mix (including Club Versions and Link Version), 3rd Mix (including Korean (v1 & v2) and 3rd Mix Plus), 4th Mix (including Plus), and 5th Mix), would also be good, if Konami can fit all of these songs on a single disc.
As for gameplay, Konami can make it more like ITG and add mines, hands, and rolls (DDR SuperNOVA: In The Groove 3rd Mix

), but that would only be good if they decide not to release any ITG titles anymore. At the very least, Konami could be more creative with freeze arrows. I have never seen any eighth notes played on different arrows while a single arrow is held (e.g. L-U-R-U-L eighth note pattern while holding the down arrow), and I haven't seen any sixteenth note jackhammers (or mini-jacks) (e.g. R-R sixteenths while holding the left arrow) while a freeze arrow is held. Those additions (at least in heavy and challenge charts) would make DDR a bit more challenging and varied.
Of course, Konami can make the new DDR games have absolutely no major improvements since DDR SuperNOVA, have the same number of songs as SuperNOVA, release them as PS3 titles, and still sell hundreds of thousands of copies. However, there is plenty of room for improvement, and Konami should always look for new ways to improve DDR.