The problem is adding Hybrid would be very hard. Also S397 is kinda busy with other stuff like the UI,Nurburgring,Updating Rain, and other content that was promised a while back. Maybe after they have their hands free to work on something it will happen or who knows it might be in development right now, but don't expect anything anytime soon. (Plus the whole "every series is going hybrid" doesn't really make sense when RF2 isn't a official game for any of those series so they don't have to focus on them if the engine doesn't allow them to represent it properly.)
What are you basing that on? As a concept it's not hard, and especially with encrypted content it needn't be overly complex (sometimes the transparency of rF2 works against it, with people assuming their other games which don't reveal any workings are more realistic or complex). I think the work S397 has been doing to organise and clean up the code as they rewrite the UI will allow them the freedom to have dual power sources; I would say that former complexity is why they had to just replace the normal engine with a battery for the formula e instead of adding it alongside.