I've seen plans (but not progress) for a Prius conversion that keeps the existing drivetrain's electric components, minus just the gasoline engine.
If I understand it correctly, in place of the ICE, a plate is installed to "lock" the engine input portion of the planetary gearset. This makes for a relatively slow-accelerating and speed-limited conversion - more of a medium speed electric car.
The original NiMH pack is also retained, and supplemented by a pair (or trio?) of Enginer/Hymotion packs and chargers.
See:
“KISS”: e-Prius Design Concept | eprius
Erik's 2005 Toyota Prius
I can't speak to the feasibility of the design. Just putting it out there.