I've often wondered if 5 Druids would be a working combination, but I'm not familiar enough with the class to know.

As for Hunters, I've got 2 of them to 70 and geared (one Horde, one Alliance) and yeah, definitely you're not going to be doing Heroic content with a 5xHunter team, at least, not very easily anyway. The only other combination I could think of would be 5 Warlocks. Soulstones for anti-wipe (this too I think is critical for any realistic homogeneous 5-group) voids/felguards for tanks and themselves for DPS.

That said, I've never had a 70 Warlock (or a 60, closest is 44) so I can't say how they'd go in end-game PvE.

The other advantage I see to Shamans to is their inbuilt anti-wipe. With a Reincarnation @ 30, from then on, I figure you'd have to better fairly unwipable (my team only 23 atm). With 5 anti-wipes an hour that's a fallback bonus no other homogeneous 5-group could match (except perhaps for 5 Paladins.......lol).