Interesting.
Re-reading the Mantle of the Laughing God, it just says he loses IC status. Looking at the BRB, IC's are still allowed to join a unit of 1 model, so long as it isn't a vehicle or MC.
So by the rules, the Farseer becomes a unit of one model, and the other Farseer can join him, to benefit from the 2+ re-roll, as well as Hit & Run.
I would very tempted to pick up a Mantle Autarch, attach a Farseer, run them right at my opponents face T1 and drop a summoned unit, and then split off as necessary T2.
In the troops section, I am also curious to know how the guardians are played. With my Eldar, I tend to take 10 guardians no upgrades, and use them as a screening and objective-taking unit, without wasting points on a heavy weapon. If anybody shoots them, its either a mistake (taking shots from somewhere else), or they arent able to shoot anything else (so a mistake on my part).
Also, on the War-Walkers front, you always want to get the 36" range where possible, it makes Battle Focus much more useful, as you can hang around right at the edge of range.
And one thing I was wondering about is are you able to give Holo-Fields to just one walker in a squadron? Ghostwalk Matrix requires all models to equip, but it doesnt say this for holo-fields.
Lastly, the Crimson Hunter exarch is a boatload of points, I would definitely recommend using the model to stand in for a Nightwing instead. With Agile & Shrouding, it has a 5+ cover save without even Jinking, and then this improves to a ludicrous 2+, and the thing only costs 145.
Would love to hear more about how this army plays out.
Cheers
Ibushi