Been wanting to look at the question of whether or not a seer council is a feasible option in the new Eldar Codex. Theoretically you could make a sort of council by buying a farseer with warlock retinue, then getting a lone farseer and joining him to the first farseer's group (although you can't have more than two farseers in normal FOC).
The fact that the net cost of most farseer/warlock options decreased in the new codex makes it look attractive at first. The only thing really lost is the 13pt boxer warlock, but this is somewhat compensated by cheaper spirit stones, wargear and psychic powers. Singing spears can now be used both for shooting and assault. At certain break points you can still get a good value on a farseer with retinue.
But IMO a couple of key rules changes that happened in the last month or so have made the traditional seer council no longer a competitive unit in actual gameplay.
The biggest change in seer council tactics comes, not from the new codex, but from the new GW rulebook FAQ
"Q: Can psychic powers...be used from within vehicles by models that are being transported?
A: Transported models are not physically on the table. They cannot do anything (unless differently specified)."
Since the new codex now specifies definitely that fortune (and doom and guide) are used at the beginning of the turn, this means that a farseer can't be embarked on a transport at the beginning of the turn in which you want these powers to be in effect. So a farseer can't ride along with a squad, disembark, and cast fortune or doom that turn. He has to wait till the next Eldar turn. Most importantly for a seer council, an embarked council can never have fortune on themselves in any turn in which they were embarked.
So a council can't be transported unless they are willing to constantly risk being shot at without fortune on (or dropping out of a destroyed transport without fortune on).
The most important change from the codex is the fact that farseers are now all independent characters. This means that in HtH combat, they can be singled out. One round of str6 or better attacks on a farseer (since he's now instakilled more easily) takes out the fortune guy, and then the council becomes much easier to bring down in following turns.
So a council can't tarpit enemy units indefinitely the way they used to. I also used to use my seer council specifically to take down units of daemons, with the ghost helm making them often hit on 5s. With that ability of the ghost helm gone, the seer council loses most of its ability in this role.
With augment gone, a mindwar council now has to close to 18" (move+rapid-fire range) in order to use the power.
With T3, farseers are now instakilled by perils of the warp attacks. That means, on average, you can expect your farseer to die once every 4 games or so assuming that he uses a single power each turn (more often with multiple powers). If you use runes of witnessing, the odds of a PotW attack increase, so that's basically an unusable item.
The only way, I think, of overcoming most of these problems is by putting everybody on bikes. They become very expensive, but they're always on the board to cast fortune/doom/guide. Boosting gets them a better invulnerable save than they used to have, and the bikes give them a save against psycannons. They can close to range for 18" powers/spears, then evade rapidfire with assault movement. A bunch of spears makes this a serious antitank unit.
So I predict the demise of the traditional walking Seer Council, except maybe in large, long-range shooty armies, and the end of most transport-mounted farseers once people realize they can't use their powers anymore. Instead I forsee a proliferation of bike-mounted farseers in most Eldar armies that use farseers. Very stubborn Ulthwe players might switch over to bike-mounted "Spear Councils" as the only remaining effective option for an Eldar psyker unit.
