Yeah I agree with the posts above, it makes good sense to hold onto your spare stones for now and wait to see what happens in WoD. That's what I'm doing just in case. I'd kick myself if I traded load of x3 stones (of a particular pet family) into 1 stone and then loads of new pets came out in WoD that I couldn't get a rare of without a stone.
For me the only non-rare pets I have are ones that I must upgrade using a stone and (as I'm sure everyone here knows) grinding loads of stones takes a long, long, very long time.
I'm going to be barking in trade for the next few months (whilst people may still be tempted to sell stones as they have loads of spares), to see if I can get someone with spares to upgrade the non-rares pets I have which are BoE, hopefully I won't have to pay much more than 1k to 2k gold for each BoE rare pet, but who knows.
Keep em, "my precious" stones are not going anywhere