Blue magic is something I would really like to see implemented sooner than later (though not too soon obviously due to the lack of mobs/skills/content). Throughout almost the entire FF series blue magic stood out to me as one of the most fun class elements. If it is implemented, however, I would prefer to not see it as mindnumbingly complicated as in XI. It should be challenging to acquire but not challenging enough that you'd have to spend days upon days just trying to get a mediocre skill.

For those unfamiliar with blue magic, it is a skill class to represent skills obtained from enemies... not necessarily being magic. Another term is monster skills.

FFV - Blue Mage
FFVI - Rage
FFVII - Enemy Skill
FFVIII - Quistis' special abilities
FFIX - Quina's blue magic
FFX - Kimahri's overdrive
FFXI - Blue Mage

I feel that with the overhaul of the battle system, some mob skills in general should be overhauled as well. Give them more skills and not make them look so generic. Enemies like the Karakul sheep are interesting with their sleep/AOE ability, and the dodos with their status effects, but most enemies seem to just attack/basic ranged attack and do some lacklustre physical attack.

If you are also a fan of blue mage, discuss how you'd like to see it implemented and what mechanics you'd have in mind for obtaining monster skills.

Edit: Oh, and Ahriman with their math skills (Level 5 Petrify), a classic blue magic sort of ability.