To answer the very last question: I am not completely sure whether they are already running, but they are in the catalog. Stadler offers Bimode and Trimode FLIRTs. At least the Trimode (electric, diesel and battery) would have In Motion Charging. And as soon as the "power module" is included, its four bays can be freely configured.
Correction to the above. Stadler actually got an order, for
Wales & Borders, consisting of Tramlink Tram Trains operating on 25 kV/50 Hz (rail network), and batteries (in the streets of the city of Cardiff), as well as Trimode FLIRTs. Actually, they label the concept as "smart electrification", because there are several stretches (with many bridges) where electrification becomes costly. So, they can run the "complicated" stretches on battery while the rest of the line is electrified.