I'm split on the OP's suggestion.
Firstly, I would not like to see multiple job pots offered to brand new players because there is no proper venue for them learn the class. For every job in this game, I believe learning come in 3 phases:
-Reading and understanding the skills.
-Solo/Role indifference practice (dummy practice/field combat/PotD/Fates)
-Group practice
The problem here is that even if you had a player who genuinely wants to learn their job, the 3rd and most important phase misses a proper venue. Players who buy jump pots for their first class, willingness to learn or not, will not be inclined to start from the lowest duty lvl and work their way up just to get group practice experience (especially if there's no hint from the game system to do so). If they're lucky, they'll end up maybe in low lvl instances several times like brayflox (lvl 32 I believe?) and get comfortable. If not, they end up in something like The Vault or some lvl 60 dgn.
And that's where the problem starts. Unless the player is basically a genius and can learn everything in one go, they will inevitably end up making basic rookie mistakes often that should not show up in a lvl 60 duty because the skills practiced on the field and the dummy, fates and PotD play out differently in a group format. TL;DR: No intermediate hall of novice, more likely to mess up in high lvled content.
And that's just ONE job.
Then there's the suggestion for multiple job pots for alts and players who played multiple jobs from start to finish. Which actually doesn't sound too bad IF--once again--the player is willing to put the effort in learning. However, the problem remains the same: lack of a proper venue (again, something like an intermediate hall of novice) for them to properly grasp the bulk of their jumped job without fear of reprisal and/or impeding other people in high leveled content. What I wouldn't have a problem with though is for example, say you already leveled a job from the ground up, like WAR and then you have an alt. Since you already know how to tank with the war and you have the money to buy a WAR jump pot, it should fine.
So to conclude, until the devs implement proper ingame thresholds for people who buy and use jump pots, I would like to see the limit remain.