Correct, that is already happening with the VW Up!:
VW Up hybrid to use XL1 tech | Autocar. Still not something that is available in the US, but the "trickle-down" is happening.
... personally I'm impressed with the XL1 FE of 112mpg ... not too shabby. If a pregen Insight *can* get 66mpg when rated for 60, it'd be interesting to see what an XL1 "can" get.
And while there may be "voodoo" in the 260mpg number, I think the concept of combining plug-in electric-only capability with a high FE ICE engine is brilliant... it's just a matter of having an equivalent method of describing that capability, as they already do for all-electric vehicles.