Looks like it will indeed be Grommloc, currently named BC01 on the PTR/Beta.
The Blizzcon page hasn't been updated with info on the contents of the goody bag, so we'll have to continue waiting for official confirmation. At this point though, Blizzard has pretty much locked this pet into place and I don't think "grommloc" will be going anywhere. :P
As a side note, he has hair. Do any of the other baby murloc-themed pets have hair? I can't remember. For some reason I find this hilarious and odd at the same time. WHY DOES HE HAVE ACTUAL HAIR?! lol