I'm not sure if anything like this was done already but I'll request it anyway.
A script that changes the game system to play like pnp AD&D 2nd edition all the things like the races, all of the ability scores, a charisma system, alignment, memorize/pray for spells, cursed items, magical + items and identification spells/lore, multiclassing/dualclassing, thief skills, weapon proficiency slots, baldur's gate 2 style class kits, etc etc.
I know there are some scripts that do some of these things but combining them into this one package might be a good idea.
Making it to where you can customize it might be good too for example not all players want their multiclass/dualclass mage characters not being able to cast arcane spells while wearing armor or have their multiclass/dualclass cleric characters not being able to use bladed weapons (hehehe gotta love some of those old dos ad&d games for that kind of freedom lol).