I think that battery vehicles with substantial batteries (and so could be run on lines without ANY overhead infrastructure in a pinch) but that usually charge via overhead lines on a portion of the route is the ideal option. No charging time, no massive new infrastructure (the catenary only needed on a small fraction of total served lines) but also full flexibility. Actually better than fossil fuel variants which need usually to be refueled at the end of the shift at a depot or whatever.

Yes, it certainly looks like a very clever solution. I know they tried the same thing with a flywheel based bus but that ultimately did not work out. Let's see how this works in practice.

It helps that batteries have literally two orders of magnitude greater range than an old school flywheel.

Yes, definitely, they are trialing this in Arnhem, I'll go have a look at it to see how it is all put together. By the looks of it they take a 'normal' trolley bus, remove diesel engine + tank + associated bits and pieces then put a battery in the spot where the tank used to be, and a bunch of electronics (regulator/inverter/charger) to create a voltage high enough to run the normal bus hardware of and to recharge the battery when the bus is connected to the overhead grid.