Aside from HP, modern-day resources have largely become specific to the job you are playing. In general, this is because each job wants to use resources in different ways making it hard to maintain a statically typed resource. MP is also effectively trending its way out of the battle system too.

Considering that in it's peak MP was used by: PLD, DRK, BRD, SMN, BLM, and healers. It lost BRD with the changes to its songs but gained RDM. However, BLM effectively doesn't use MP since it innately levels itself out. PLD barely used (and uses) it, and DRK just siphons it and innately levels it like BLM. RDM for most of its lifespan hardly worried about MP unless it became a raise turret. In its DoT peak, SMN was left as the only damage dealing job that made thoughtful and careful use of MP over a long period. Healers (mostly to this day) are much like BLM in that their job auto levels their MP using their job mechanics (there are outliers, yes).

In the modern game, PLD really doesn't need to worry about MP at all unless for some reason it needs to become a holy healer turret. DRK and BLM auto-level their MP usage. Healers, in general, have MP management tools in place that sustain them (again, some outliers). This leaves RDM and SMN, but as long as Lucid Dreaming is used frequently their MP usage is much like BLM. On death, only healers will majorly struggle coming back to full usefulness for their role solely due to MP. Even when RDM and SMN become raise turrets that will not cut them off from doing damage due to low MP, they simply can no longer continue as a raise turret.

I may be oversimplifying and stretching some points, but the main takeaway is that jobs are moving away from statically typed resources to dynamically typed resources that are specific to their job. This is very evident based on the continued explosion of job gauges and resources. So, instead of bringing back the staticness of TP and aggro, perhaps suggest ideas that are more specific to the jobs these resources used to affect and make them rewarding for that job's system.

No one really cares for the TP system because it worked the same way for all tanks, melee DPS, and ranged physical DPS. It restricted them all equally too. Aggro was a function of specific combos but also relied on other party members doing something that only benefited the performance of a tank (which also included melee DPS and ranged physical DPS casting "aggro shrouds" on others). Instead, maybe a PLD has to use various oaths for future attacks (alongside sword oaths). Or maybe increased aggro is a result of using a Fell Cleave on WAR. For resource management in general, Square Enix could easily keep developing the specific job resources already in place and expand them to more actions with increased benefits and rewards for that specific job.

I can easily see MP removed in a future X.0 release replacing it with more burden on job-specific resources.