Mercule
Adventurer
I actually wasn't a huge fan of the Bo9S. I did like the ToM, though. I don't like Far Realms, per se, in D&D so I use the GOO Warlock patron as a Binder. I could use more vestige-based Invocations, though. I think a Shadow bloodline for Sorcerer or a Shadow patron for Warlock (probably the former) would be good enough for the Shadowcaster. I'd love to see this. The Truenamer, while a staple of fantasy fiction, just didn't seem to really work in D&D. I'm not hot on seeing it retried.I'm surprised no one mentioned "Book of Nine Swords" or "Tome of Magic" classes from 3E.
The class I'd really like to see show up with the Mystic is a new Ardent. I like keeping Clerics as servants of gods, but the Ardent was really, really nice for having a "priest" of a philosophy.
Of course, as an Eberron fan, I'd also really like to see an Artificer class that captured the feel/niche of that class. The most recent attempt was completely inappropriate to Eberron, which immediately disqualifies it as an Artificer, regardless of any other qualities.