If the leaks are true, Blue Mage will be a support DPS. If that's the case, it may very well be a Scouting DPS like Ninja. If implemented as such, they'd make BLU a DEX melee DPS with lowish personal DPS but high raid utility.

It seems that each DPS archetype (as evident by gear) share some similarities.

Striking: High personal DPS, low raid utility.
Maiming: Moderate personal DPS, moderate raid utility.
Scouting: Low personal DPS, high raid utility.

They can easily make Blue Magic based on DEX similar to how Ninjutsu is based on DEX (and PLD magic based on STR).