Have you played Disc priest lately? They are a bit more complex for healing compared to others, but with four that might not be an issue.

In WoD, their DPS was just so bad I would have hated that group composition. Mine did 7k-9k, ugh horrible. One true DPS would out preformed all four Disc priests.

You might want to check the discussion in the thread here:
http://www.dual-boxing.com/threads/5...team-in-Legion

Restro shaman looks really nice for healing. Possibly going 4 elemental shamans would do what you want and you could just switch one to Restro if you need the true heals.

Love the Pali tank, I think the majority are going with that for Legion. I think going 5 pali tanks would be way better DPS and survive longer than Disc priests, and still let you in LFG.