I know this would be very hard to implement but the need is surely out there.

It's not uncommon to let the players change the UI to some extent or write graphical tidbits that collects and display information on the screen. It would help players to redesign parts as they would like for a more fluid experience without the need to ask the dev team to do it.

Graphical spellbar with timers? Yup. DPS-statistics. Yup. Overlaying timers on buffs and add debuffs on players. Yup.

The system don't need to be perfect, it can be a bit hard to use. Players will manage after all. Take a look how other programs implement it.
* You can mostly only pull information from the API, not send information to it.

Other MMO's have implemented this and it's a sought after in FFXIV. So why not in FFXI?

I understand that this will take time to implement and would need a lot of adjustment, and hopefully FFXI is still here when this can be introduced!