One other advantage to having a good selection of clanless schools would be to make a single-clan party a lot more viable. For instance, if you have a Lion party and more than one person wants to play a Matsu, some can take clanless schools so everyone doesn't end up with the same techniques.
This would make it a lot easier to play in certain time periods, like the Clan War.
EDIT: This would also open up the possibility of playing single-clan court-based campaigns, which are normally kinda stale since everyone would be funneled into the same school.
Edited by Fumi