Speculation and nothing more.
Comicon Hasbro panel: "Weird Al back in soundbooth", "product for season 3 under production". Comicon IDW Panel with Marty Isenberg: "Fall 2009".
Before that we had character designer guys blog with the preview square showing off Jetfire and Jetstorm (along with S2 guys like Swindle and Shockwave) wich are promised to pop up in S3. Guys at Botcon saw those, Arcee and Perceptor.
David Kaye confirming the BW story guys being involved in the season.
S3, while not say confirmed Cartoon Network airdate seems pretty friggin under production to me.
Wich doesn't mean you can't take these with a pinch of salt. I know nothing of this S250 fellow.
The Decepticons in a state of dissaray over half a universe is pretty ripe for shaking up the roster of the last two seasons anyhow.
In any case, even if many of these guys are cameos or background characters to beef up the toy isles this is PACKED.