Thoughts on Custodian:
The Kororvesh fleet has some unique flavor traits. Equal shielding to its counterparts in other fleets, -2HP due to lighter more efficient construction, 90* turns, and a greater concentration of turrets. These things set a tau vessel in whatever ship class it falls into.
Thus, the Custodian needs a 90* turn, and at least the option for an extra shield and turret at a points increase.
This is for flavor and fleet cohesion, but it also goes a good deal towards perfecting the ship at its role in the fleet, as a more hands on carrier than the Explorer.
Thoughts on Protector:
If it were up to me, Protector battery layout would be 4/4/4 and become 3/4/3 and forward locking lances for the variant.
Still feel its overcosted, 170 point ship at the high end. All systems firing forward, slightly surpasses the single broadside of some cruisers.
-2 HP is a big disadvantage to other line cruisers. Nature weapon positions means its almost always going to suffer the closing column on gunnery chart. Try and reconcile that with 5 points more than a Lunar.
Thoughts on the Emissary: I guess its accepted that the fighter bay variant is purely for fluff and fun, so be it. 2 and it would be a fine alternative. Otherwise, probably the best capital ship for its points in the fleet, great example of a good ship.
Option for extra hull points or extra shield would be appreciated.
Thoughts on the Castellan:
Pricey but solid escort. Wish it had a tad something more for 50, as Id much rather pay the 10 points for an Emissary over 2 Castellans, for many reasons. Wish it had an extra weapon battery, and lost 5cm of speed, at such a premium points level. Those huge escorts also LOOK like they pack more firepower. Lose the 90* turn if its overpowered, the thing feels and should function like a long range artillery piece. Or make em 55 points.
Thoughts on the Warden:
I've come to accept the little fellow. Not quite Orca levels of cost/effect, but the slight improvements make it still a great steal for 30 points.
Don't change a thing

And for fun, anyone seen this yet?
http://forums.tauonline.org/other-gw-games/61732-tau-bfg-experimental-ships.html