Tbh that's a bit shitty. Either you're a casual guild and then it doesn't matter, you can play with ferals, shadows and shammies and still clear raid. Or you're hardcore and then probably those shamans would think themselves about a backup plan and discuss it with the guild, because shaman has notorious history of being bad especially starts of xpacs. I know our players from "dangerous" dps specs planned a backup, ele shammy made a warlock and spriest made a hunter. And ended up they're playing these alts until their mains become useful in mythic raiding. Sad but true, check logs for fetid devourer mythic: nearly 400 warlocks and hunters, 25 ele shammys, 6 enhance and 21 spriests. Shows which classes are not picked.