I think really they just need to implement some kind of plug-in or extension framework. Extensions are just not first class citizens but they really should be.

There should be a .gitextensions in the repo that the repo owners maintain just like .gitignores and . gitattributes etc etc. Everything can still be opt in by every user but at least all git clients would be able to know about, pull down, and install per user discretion.

It seems pretty basic in this day and age but it's still a gaping hole. You still need to manually call LFS install for goodness sake.