would be pretty surprised if they use the W12, as its a pretty "old" design now. The new 4.0 V8 turbo (based on the RS6 V10 twinturbo iirc) is a more likely candidate. And its the engine that replaces the W12 in the road going Continental.
There is only one W12 (from VW) in racing, in a Ultima-like Kit Car in the Netherlands, can't remember the name tho.
With all those GT3 manufactures, start a damn real GT World Cup :headbang: