The chances for DS9/VOY in HD are probably better, if the conversion team behind TNG in HD learned a lot about optimizing the process with the TNG material. After that, converting DS9 and VOY is probably much cheaper than it is with TNG right now.
DS9 and Voyager will both require a massive effort to redo all of the CGI work from scratch. They'll both be much more expensive to bring into HD than TNG will be, while they bring in much smaller profits.
That's why it's so unlikely (but not impossible) to happen.