Thinking of a Mod that overhauls the static leveling system with an experience pool, does this already exist or not, and how do you balance Prestige Classes?

If it doesn't then I might commission one for both games but basically:

• Instead of just going through 20 levels at static benchmarks, you get an experience pool.
• If you want to level up a Class, you have to exchange experience at the 'usual' rate, but each Class is leveled separately from the others. (First level is 1,000xp for this.)
• Leveling an Archetype is either a one-and-done replacement of the base Class, treated as a separate 'Class' from the base Class, or you pay a smaller fee to add each new 'level' of abilities specific to that Archetype to your base Class as they become available.
• Your BAB is limited to your highest-BAB Class per level for the sake of balancing.
• For instance, a Level 7 Sword Saint Magus who just got 5.25 BAB might delay their 7th level (16,000xp) to spend 6,000xp to level Fighter to 3 for Bonus Combat Feats and an additional 0.25 BAB for their earlier levels, raising them to 6 BAB for ~1/3rd of the experience.
• Not sure how leveling a Prestige Class would work, especially with CL in mind. Casters are tricky to balance versus a 20 BAB limit, unless you let Prestiges raise the BAB limit too... then they become a quick-and-meta way to raise your BAB/CL and everyone uses them. Maybe their xp cost scales multiplicatively with their Class, or raises future leveling costs for that class? Or just make leveling over 21 only possible if Prestige Classes are involved and they're super-expensive to compensate (if you really want that Aldori Defender20/Swordlord10/Duelist10)...

Opinions, thoughts? I know it'll be overpowered no matter what, but let me have my fun. You can always customize the difficulty or just mod that higher too anyway.