I know you've said in the past that you want Job Points to be earned per job, but there's a flaw in this line of thought: People that really commit themselves to certain jobs find they're always in demand on that job (WHM, GEO, PLD, RUN). Other jobs just aren't very welcome or welcome at all in a lot of CP parties (SMN, RDM, BRD).
I have a very well rounded Paladin. I have gear sets for every situation and many sub jobs. I feel like the best way that I can help my friends is to be taking the hits, knowing that I can handle them better than any of them.
On the other hand, like Bard in days past--if you have an Idris, you may as well mule your other jobs, because people will want you on GEO.
The same desire for, and exclusion of, certain jobs existed in merit parties in the past (BLM, BRD, PLD, THF really weren't welcome at birds--everything was RDM, BRD, SAM, WAR, NIN, DRG, etc) but it was easily remedied because you could gain merits intended for one jobs on other jobs.
It's to the point I cringe when my Paladin or Blue Mage gains a job point. (BLU is very nearly capped, more than 400 JP over cap). There's nothing I can do with them.
I'd be fine if it was a conversion rate even, or something we set in a menu. Job Points > Earn for > [Job List], even if the conversion worked off of the target job's JP gifts (this would actually be ideal). So say I want to earn 103 JP SCH while on my 2100 paladin--I'd gain job points at the rate my SCH would earn them, not my PLD.