This could be a solution.

starting from GreyJorildyn idea, I quote myself:
They could very well increase the lvl cap for jobs only, though. Wouldn't be a bad idea, imho.... expecially from abilities point of view... if you increment lv cap for both jobs AND class, you will need to think of new abilities for both and this could lead to difficult balancing, since the class abilities will have to be shared with the multiple jobs (coming from that class), but also with the jobs "importing" abilities from that certain class (e.g. like MNK gets abilities from LNC).
at LV50 jobs are very similar to classes, but then, you can bring them to (let's say) LV75 and you have 25 levels worth of unique abilities tied to that, and ONLY that, job.