Pretty certain it's an electric-only version... for now. RSC will be updating it as and when development advances on the real thing. I certainly haven't found a way to switch to alternative power modes, and in any case I think the real-world specification for the hybrid versions of IEP calls for electric underfloor motors and a HST-style "power car" (i.e no passenger compartment) at one end for diesel power, which we currently don't have in the sim. I could be totally wrong, although that would be a first (!)
JB