I doubt that Lamborghini will go and make a V8 Gallardo. Audi and Lamborghini must make sure that they are offering different cars. I bet that if Lamborghini produced a V8 powered Lambo it would cannibalize on sales for the R8, the same as if Audi would produce a V10 powered R8S (or whatever the automotive journalists are calling the V10 version these days).
In an interview with Stephan Winkelmann about Lamborghini’s future and in it he talked about Lamborghini wanting to reveal a new model or an evolution of a new model each year.

http://lambocars.com/new/interview.htm

Still I think that the best bet is that the Lambo being tested at The Ring is an evolution of the V10 engine, maybe with a new exhaust system on it.