Grey Knights to Tyranids

If Grey Knights become Tyranids in 2014
there are a few options that people may want to comment on.

Here is the suggestion:-
They are of the same Tyranid hive fleet tendril
battles lost by the either Tyranid player will result in any Tyranid lost hex.
They become one fourth player in the Hex Campaign
but they are able to fight two battles on one night.

The Grey Knight hexes are taken over by :
Tyranids (my preference).
or The Warp (all hexes become impassable).
or Held by defending Grey Knights (who can no longer attack).
or Divided between all four players.

Please leave any comments for discussion...