Since we still have no idea of when the DA15 is going to be coming out, nor have details about the specs, I would say go ahead and get the DA21. Since we don't have any more info than we do, I would suspect that the earliest that the 15 would come out would be sometime next year. With the current (3/18/08) lens roadmap in mind, I figure that the lenses yet to be released will come out in this order:
DA17-70/4 (we've already seen pics from Ned's test copy of this lens
NED BUNNELL: DA 17-70 Sample Photos)
DA*60-250/4 (on the roadmap, it has a targeted availablilty date of summer 2008)
DA*55/1.4 (on the roadmap, with an aperture speed, but marketing date to be announced later)
The following lenses are on the roadmap, but with not much in the way of details and no tenative release dates, so there's no telling what order they'll be released in:
DA15 Ltd.
DA*30 SDM
Rear converter for SDM
The *55/1.4 piques my interest, but that's not going to stop me from buying a 50 in the meantime. I figure that once the 55 comes out and I decide that I do want it, I can always sell the 50.
Heather