We can only hope. The ISBN really does grant it an air of legitimacy, and with NDA's and the like, I can see of course that they would deny it before it was officially announced.
I like d20, I like Star Trek. I would love a Star Trek d20 game. The old FASA game was a disaster, the Last Unicorn Games version was pretty nice (I have almost all the books for it), but Decipher's just didn't seem to have that same spark.
Mongoose proved with the Babylon 5 RPG that they can make a fine licensed sci-fi RPG, and I'd definitely buy a Star Trek one if they made it. (of course, I doubt Paramount would be as cooperative with the creative side as JMS was with the B5 RPG, but they've shown they could do it well)
Paramount/Viacom is known for being a total sell-out when it comes to the Star Trek license, they'll put it on anything if it'll sell, so the Star Trek RPG license is doubtless to not die just because Decipher did. Even if Mongoose doesn't pick it up, it won't lie untaken indefinitely.