Optimus almost had his own miniseries, but Dreamwave went under before they could get that off the ground.
I don't know if I'd want a miniseries focusing on one character for multiple issues as much as I'd like a pseudo-anthology series that centered solely on one character per issue. One issue they do a solo adventure starring Skids, the next they do Skywarp, then they do Omega Supreme, etc.
Transformers has such a vast selection of characters, assuming the stories are good enough, the series could go one for hundreds of issues. Plus it would give the fans of those rarely-seen specific characters something to chew on.