I was just speculating on this the other day (not realizing WGTC was speculating about it too, but no surprise there)... While Brooks hasn't really been acting for some time and didn't even contribute to the DS9 documentary, there is one reason why I think there's potential for him to come back.
One of the things Brooks most values about DS9 is that it portrayed (in his words) "the relationship of a brown man and his son." It was a show that showcased an African-American man being a responsible father (a single father, no less!) with a good, strong relationship with his son at a time when that wasn't commonly portrayed on TV. But it ended with Sisko leaving his newly-pregnant second wife to care for responsibilities elsewhere. If memory serves, the "I will be back" was added at least in part at Avery's insistence so he wouldn't be abandoning his wife and child, at least not entirely. (Remember reading that in the DS9 Companion, but I don't think I have a copy anymore, so can't confirm.)
I have a hard time imagining coaxing Brooks back as a series regular. But a TV movie or a guest appearance that establishes him being reunited with his family and acting as a father to his sons regardless of his responsibilities to the Prophets? Especially if they set it up in a way so he hasn't been gone for 20 years? That I could see him going for.
