Crossed posts with Mark...
Most of the dual mode trains in use in other countries are long distance passenger or freight trains, and in many cases they have a small diesel generator so they can make it the last few kilometres on unelectrified tracks.
I agree it's a pointless idea for urban rail.
One interesting idea being tried in the UK is inserting an electric car with pantograph into the middle of an existing DEMU to turn it into an dual mode EDMU. As far as I know the 22Ks are straight DMUs rather than DEMUs, otherwise this might be an option for them.