I'm getting really sick of the pagan bashing on the forums. I for one, fully support and hope for a pagan dlc, I have ever since SoI was announced. They really need a overhaul. Right now they're a free landgrab for the christians. No flavor or unique mechanics put in to help them out whatsoever.
I think Norse could get a head of faith, as there was a chief religious figure of sorts. And these arguements against an earlrier start are pretty laughable.
Guys, The folks in the mod forum did Terra Normannorum that sets the date back to 1000, and they did it well. There's also Novum Milennium. The fact there are two 1000 start date mods shows this is possible for a DLC. 1000 is also an extremely good start date because it takes place shortly after the Personal Union of Denmark and Norway. You could even set the start date back to the 990's to play as the Norwegian tyrant and stop Denmark's alliance, thus changing history in a pre-set war just like the 1066 start.
You don't have to set the start date back 100 years, the start of the 1000's has enough plausible records and history to be done, You could also include the Hungarian magyar pagan chiefs and counts under the catholic ruler, 1000 AD Hungary and Poland both had a serious possibility of going back to Paganism at that period of time.