I like the idea. I'd rather have my adventurer plate portrait be displayed though.
Why is maching gear and job on a portrait even a thing? Who cares if I'm wearing Summoner gear on a portrait while doing a dungeon as a Reaper? Or if I'm using a job-specific pose, while not being on that job?

Certainly not because of immersion, considering I can slap a Namazu head on my character just fine.

This is such an unnecessary, annoying restriction to have.

Just let us design tons of portraits and attach them to gear sets. No restrictions >.<.