I wouldn't mind a Time Mage. Yes, AST incorporates elements of Time Mage, but at the same time, I think a Time Mage could work by itself as well. A DPS oriented class rather than a healing class. Not unlike how SMN is a DPS version of SCH. I also don't care much for Astrologian and its Fortune Telling gimmicks, so a Time Mage would just suit my personal tastes better.
But I don't think we're getting Time Mage in 4.0. Maybe 5.0.