In battle Class switch

[Cadwgan]

The dungeons and raids are designed to be playable with pretty much any combination of classes anyways.

No, they aren't, at times you're required to bring classes that can do specific things (e.g. silence high voltage and earthshock, restore TP and/or MP), whole reason why they added coil nerfs when it became DFable as you can't guarantee certain setups in a DF group.

You could change jobs at any time in 1.0, including in dungeons and the result was people demanding you had a combination of jobs X, Y and Z levelled and geared or you aren't joining. While I agree it would add a bit more variety and allow for more minmaxing but people being assholes demanding specific job combinations is why it was nixed in the first place.

Saying that, I wouldn't be opposed to a "request/vote to job change" you can use a set number of times in dungeons where members can request to change jobs then have the whole party approve or decline the new setup, would help when tanks and/or healers drop when a DPS has the ability to switch.