I'm making the Ability Focus feat in srd35 work for character sheet math instead of outputting a result from a CHOOSE:STRING, which is an absolute bear (compounded by the fact that many valid abilities don't have variables for their DCs, so I need to MOD them when they come up).
I'm not killing myself over this: just doing it on an as-needed basis. But, I realized how easy this would be if they were treated like spells. I could just do a BONUS:DC|ABILITY.<Whatever>|<Value> (or something) and be done with it, instead of having to define hundreds of unique variables across a dozen sources. Especially if we could put multiple requirements here (BONUS:DC|2,CATEGORY=ABILITY,TYPE=MindAffecting|<Value>).
I deal with changing DCs on abilities all the time (with some solutions that are even more inelegant than what I'm doing for Ability Focus), so I imagine it would have great utility.