FWIW, if you took the most recent player's poll, it sounds like they might have a general concept for the RDM. One of the options from the "what new classes do you want" question was "A new type of magic-user that uses enfeebling magic and close-range attacks. (ex. Red Mage, etc.)".

I find it unlikely that from a game mechanic perspective they're going to fit what people imagine as a traditional Final Fantasy RDM "jack-of-all-trades" (as a career RDM or hybrid class player, I hate hate hate that term) which is going to melee and cast both Cure and Fire. It's possible, but... that's how FFXI's RDM ended up where they ended up.

And in general, doing hybrids well in MMOs and having them not either be strictly worse than bringing a dedicated class or totally OP because they can do everything is really hard. Hybrids work well in games with small groups but when you start getting to large-group content stuff kinda goes out the window. You can sort of pull it off by either having state-based hybrids (see Scholar from FFXI or Druid from WoW) or cheat by giving them something absolutely necessary (lolRefresh) or a totally different role in large group play (crowd control is one example).

All that said, like a lot of people I would totally love to see something that looked a lot like Dancer, which used one set of abilities to build up a resource which gets expended with a different kind of ability. Honestly, as long as there is the base flavor of having something that looks like fencer-y melee skills (these may or may not actually be real, TP-using weapon skills) lead into something that looks like magey spells (which may or may not be real, MP using spells) I will be happy. Frankly, even if the only magic they get at all is debuff spells I'm fine with that; I'd much much rather they err on the side of magic-fencer flavor than jack-of-all-trades flavor.

My only other big concern is how they solve the itemization problem so they don't end up being magic fencers in stupid mage robes all the time.