ToME WikiDescribe Developers Corner/Proposals/Playable Dragons here.
If Orcs, Kobolds, and Deathmolds are playable, I see no reason why Dragons aren't playable either. They'll have to be either innately gloved or bipedal, as quadrapeds will have a great deal of difficulty performing alchemy...
Derakon: Play a Possessor who specializes in dragon corpses. Unfortunately this does limit you somewhat as far as class is concerned.
Aren't the races and classes already specified in resource files? I see no reason why you couldn't do this yourself, right now. Just copy one of the existing classes, take a look at the Deathmold specification to figure out how different equipment slots work, and have fun.
NeilStevens: Please move these over to the IdeaArchive, thanks.
NerdanelVampire: There are already playable dragons in several modules such as Annals of Ea and Theme. You might want to take a look at those.