I think some of the confusion lies in the way the rift works. The rift is already integrated AFAIK into the cry engine. There are plenty of games out there that have native rift support. Hawken, HL2, TF2, Warthunder etc. they are playable in both normal mode and in rift mode.
All rift mode does is split the screens and allow the 3D stereoscopic view to be projected to the rift. When I say that it should be the main form of delivery, I mean dedicated focus should be put into optimizing the game play, controls, head tracking and graphics for the rift.
This does not mean the game will be rift exclusive. I don’t think warhorse is foolish enough to do that so early on in rift development. If you choose to play without the rift, you can, and the game play is no different. Having a properly integrated rift does not negatively impact the game for non users, it simply enhances the game for those that choose to play in stereoscopic 3D.