The fact that DS9 was assembled on videotape - like TNG and the other modern Treks - actually means that "remastering" for HD would be so hellaciously complicated that it will probably never be done.
With TOS, film originals of the episodes exist. With the modern Treks, all that exists on film are millions of original shots, pre-editing. Actually, to say that they still exist, much less could be transferred to HD and then edited to recreate the shows, is an optimistic assumption.
The only Trek we'll see in HD other than TOS is the final season of "Enterprise."