Interview I read mentioned reboot also, but said that they'd bring Optimus and Bumblebee along. But they've introduced new bots and killed off some (Iron Hide, NOOOOOOO!) so there's always the opportunity to bring in new ones.
I've mostly been okay with the films, robot on robot violence and all that, but man, they do not hold up on a second viewing. I really kind of enjoyed DotM when I saw it in the theater but when I saw it again on DVD I couldn't remember why I'd liked it so much. There's just too much to pick apart on those films and it all seems to really stick out to me on replay.
GI Joe was the same way. I mostly liked it the first time but the second and third times I saw it all I could do is look at all the terrible CGI. And I still can't get past the sinking ice. There's only so much suspension of disbelief I can apply to a film like that, and the total suspension of the laws of physics was not something I could do.