I know that we have enchantments that cause weapon speed to increase, but I was wondering if there was anything that caused casting/blessing/chanting (referred collectively as 'casting' from here out) time to speed up (or take less time, however you prefer to think of it).

It's an interesting idea, but from a game balance perspective I don't think it'd work without substantial other changes. What other enchantment would a caster possibly use if the option to cast devastating spells like petrification quickly was available?

Being in mood aggressive speeds (or at least used to) up the casting time of most if not all spells.

I think recent flying changes slows casting down.

EDIT: Scrolls, wands and staves have lag time after but no start up time, if you count that.

Or perhaps there should be a new skill introduced called 'concentration'. The lower the skill, the harder it is for the caster to cast when there's lots of commotion/fighting around... resulting in longer cast times... whereas the higher the skill, the ability to focus more during commotion leading to quicker cast times.

It is not documented entirely, but this functionality already exists somewhat. Ask around in-game, and someone can give you information that's had the serial numbers filed off properly. I can only give you blatant OOC info.

No it doesn't, and it never did. I argued strenuously that it should when stances were first implemented, but it was never implemented. Stance neutral/aggressive casting times are the same. Defensive has extra lag.