Just for funsies a little while ago I did my own "What would the game look like if we removed Constitution?" write-up... and substituted 'Perception' as the CON replacement ability. So the third physical stat was now all the sensory (and extra-sensory) organs taking in information, and thus I would then use Perception as the Ranged attack stat (as Aim would be its primary "thing"). People always want to reduce Dexterity's ubiquity, and giving Ranged attacks to a different stat would be a good first step towards that. And Perception was an intriguing option for that (and it didn't hurt removing it from the skill list, as its easily the most popular and taken skill in the game.)
What adding in Perception as an actual ability score did was allow me to then take the 15 most-standard/popular classes in the game (the base 12 plus Artificer, Psion, and Warlord) and assign them to each of the 15 ability score pairs to make every class MAD. What I ended up with looked like this:
STR/DEX: Barbarian
STR/PER: Ranger
STR/INT: Warlord
STR/WIS: Fighter
STR/CHA: Paladin
DEX/PER: Rogue
DEX/INT: Artificer
DEX/WIS: Monk
DEX/CHA: Sorcerer
PER/INT: Psion
PER/WIS: Druid
PER/CHA: Warlock
INT/WIS: Wizard
INT/CHA: Bard
WIS/CHA: Cleric
Now granted, this did lock in a few classes to certain directions thematically that they otherwise used to have multiple ways of going (for instance the Warlord would now be more like a Tactician now that it no longer really had a CHA option, and the Ranger would be more fighterish than rogue now that they were STR-based without a DEX option.) But at the end of the day I didn't really concern myself with those locked-in directions as this was purely for "What if?" entertainment on my part and its never actually happening so it doesn't matter. But it did give an interesting direction where things could go if there was ever a bigger slaughter of D&D sacred cows down the line.
What adding in Perception as an actual ability score did was allow me to then take the 15 most-standard/popular classes in the game (the base 12 plus Artificer, Psion, and Warlord) and assign them to each of the 15 ability score pairs to make every class MAD. What I ended up with looked like this:
STR/DEX: Barbarian
STR/PER: Ranger
STR/INT: Warlord
STR/WIS: Fighter
STR/CHA: Paladin
DEX/PER: Rogue
DEX/INT: Artificer
DEX/WIS: Monk
DEX/CHA: Sorcerer
PER/INT: Psion
PER/WIS: Druid
PER/CHA: Warlock
INT/WIS: Wizard
INT/CHA: Bard
WIS/CHA: Cleric
Now granted, this did lock in a few classes to certain directions thematically that they otherwise used to have multiple ways of going (for instance the Warlord would now be more like a Tactician now that it no longer really had a CHA option, and the Ranger would be more fighterish than rogue now that they were STR-based without a DEX option.) But at the end of the day I didn't really concern myself with those locked-in directions as this was purely for "What if?" entertainment on my part and its never actually happening so it doesn't matter. But it did give an interesting direction where things could go if there was ever a bigger slaughter of D&D sacred cows down the line.