At LOG, Roger Becker stated that the engine for the new Esprit could be either a V8 or V10. The new platform is designed to accommodate either.
Which one has not been decided nor has Lotus committed. (He was definitely asked about the BMW engine.)
One thing that is holding up the selection of engines is future EU emissions laws, specifically carbon emissions. With all manufacturers having to reduce CO2 emissions by about 20% in 2010 - 2011, a big CO2 emitter might make the Esprit non-salable in Europe...