With DS9 though, I am not so sure. The show was never has popular as TOS or TNG, even in its prime, and at times it becomes a blacksheep amongst the core fans of Trek aswell.
That statement is made more often, but has no real basis in fact. It did have lower ratings, but at a time where ratings for SF were going down already. Someone posted a graph for Star Trek ratings since TNG, and it was a decline at one point for al series, Star Trek as a whole was becoming less populair.
As for DS9 being the black sheep..... The only fans making comments like that, are fans who feel that TNG was the last REAL Trek, and there are fans who feel everything after TOS is not real Trek. It depends on who you ask.
If you ask around on this forum in general, you'll find that DS9 has a huge fanbase. Now, wether or not this is enough to warrant a HD remastering.... Let's hope so.