If you think about it, it was never job changes but first jobs.

Y'shtola was a conjurer, Thancred a rogue, Urianger arcanist.
Now Alphinaud finally gets one as well, going from a fake Scholar job.
You could debate that Sorceress is something else than WHM and BLM slapped together and therefore not a job.

But I don't think they will change soon, except if a new caster job that completely fits Y'shtola happens to be introduced.

If I remember well, Yoshida mentioned that the character going to the next arc will depend on their popularity. If Y'shtola is tiring the community, she might just not (or rarely) appear in the next arcs.