The Tau leader is a kor'o, i believe, and can be played on the Custodian.
Named Leader
Ld 9, 1 RR + Aun friend in cost(1RR) + Skilled pilot (I don't know what that is, heads up Dan, if you're removing keywords)=110pts, with an aditional, optional 10 point upgrade.
OR
Kor'o + standard Aun
Ld 9, 1RR + Aun(1RR)=105pts
So you're paying 5 point to have skilled fighters, seems like a sweet deal to me! then maybe I'll use that optional, maybe I won't.
Not saying that He should or should not be included, just that he's not expensive compared to the normal cost of leaders for Tau.
I know it sucks that you have to buy a big base, but is that the only reason we're leaving it as an optional instead of just making it an automatic 3 shields? I think in the old BFG:R it was automatic already, and I think it should be again, to homogenize grand cruiser rules.