I have seen quite a few vids of little stealth groups doing quite well in PvP action. I think it will be a very popular build.
I'd like to build a character dedicated to killing this group. It would be handy for Keep and outlying buildings defense and a fun solo build for Cyrodiil. A DK with a Magelight is the simple version. He has to be able to take a full stealth bow hit and immediately engage the target. There are a range of DK abilities I think would be ideal for this purpose.