There's bound to be a DS9 Bluray release. Most of it was filmed - even the FX for the first few years, so it's suitable, although the last few (2 ?) seasons will need new FX to replace the lo-res CGI. Or so I heard... Costly, but less so than Voyager which is apparently stuffed as it's all CG'd and would need a complete do-over.
Trek series have to keep being reissued to keep earning money - it's just that the less popular shows don't have the sales to make it worth it until costs drop. That's why Enterprise has leapfrogged the other shows - it's already pretty much ready for Bluray already so despite it's lack of popularity, it's cheapness makes it worthwhile releasing next.