Im so excited! I re-subbed just for RDM. I have been complaining since 1.0 because i wanted a spell-sword(not pally or drk though i like drk). I think it will be mostly obvious how it plays with all the info we have. There really arent that many options if you consider the game balance and current mechanics as well. First off If Yoshida said pure dps.. then no heals. Then we can only assume:

It uses speedy positionals.
Chainspells -assumption: cant be a fancy name for 123 combo. or they would have said combo...right? There has to be something else to it.
Black Magic -assumption: Combo finisher that is something like a Flare from BLM
White Magic -assumption: Most likely Aero or something damage based from the WHM job. If not damage based, and not a heal, whats left? Stone? Esuna? Cant be.. hm..Haste? Wait, speedy positionals.. hmmmm...

Im willing to bet RDM has Earth, Fire, Lightning, Water, and Aero spells from WHM/BLM or a 123 spell combo of similar type magics. Im betting that RDM builds stacks similar to monks greased lightning with those spells in ranged positions. As well as lunging abilities to get in, or out of melee range and dodge larger aoes. It will most likely be squishy and die fast. It will probably use magic based melee attacks that can keep the chainspell stacks flowing.

Another possibility for chainspells is something like warrior's wrath stacks. Spend your wrath to use an innerbeast type move.(The flare thing)
Or...
Ninja-like: What skills you use, and in what order cause different end results to be cast.
Either way i can hardly contain my excitement until summer x_x