This probably has been dicussed, since the coincidences are obvious, the antlers theme everywhere (I recall that one of Hircine's aspects back on Bloodmoon had a moose/deer head), that you need to cut those hagravens heads (and it seems that the hags are somewhat in league with the Forsworn) to cure Lycanthropy, the skulls and blood altars (throphies no doubt). I propose that the Forsworn are actually a tribe of bretons that went on to settle on Skyrim, found life too difficult there and turned to Hircine for protection.