The official name of the train is "Alstom Coradia iLINT". The original LINT (Leichter Innovativer NahverkehrsTriebwagen, roughly translated "light innovative regional motor unit") was built by the German company Linke Hoffmann Busch, which got acquired by Alstom.

Most LINT DMUs are operated in Germany, by DB but also private operators. Some exports went to the Netherlands, and to Denmark. There is one overseas operator, O-Train in Canada.

There are four types of LINT out there, LINT 27, LINT 41, LINT 54, and LINT 81. The number signifies its length in meters (the type O-Train is operating is a 41).

The Coradia iLINT is based on the LINT 54 model, consisting of two cars with two bogies. Three of them are driven by a 390 kW diesel motor via a mechanical gearbox. Maximum speed 140 km/h.

Now, we get closer…

The two trains currently getting in use in Niedersachsen have two driven bogies (essentially an electric motor instead of the diesel with gearbox. Each car has its own fuel cell, and a 55 kWh buffer battery.

On level track, the energy provided by the fuel cells is sufficient for traction and auxiliary drives, and there is some little excess which can be used to charge the batteries. For accelerations, energy is taken from the battery, and regenerative braking will charge the battery.

So, the 1000 km range is based by almost level tracks, and intelligent use of the regenerative braking. I would consider the trains to be poorly powered (sufficient for regional services on lines without significant grades). This is absolutely fine, because they are prototypes (even if the operator has a total order of 14 units).

For S-Bahn applications, the current train is definitely underpowered, and I am not quite sure whether there would be enough space for all the equipment in a bi-level design. In any case, all axles would have to be driven. OTOH, there is nothing speaking against MUing three or four such units, leading to 6- or 8-car trains.

Whether Fuel Cells are economically and ecologically viable has still to be proved. The main question is where does the hydrogen come from. If it is created from water, using electrolysis, the electricity has to come from somewhere, be it from wind farms, be it from coal fired power plants. Another method uses Methane as base, but that process is not CO2-neutral. Ideal would be if there would be a factory nearby where hydrogen is a by-product, which would otherwise simply be burned off.

You are absolutely right, that iLINT would be very suitable for SMART or eBart. About the latter, I am pretty sure that the engineers in Bussnang are working on a power module for the GTW and its successor, as well as for the FLIRT. If it were ordered by the operators, it would be quite easy to replace the power module while keeping the rest of the train as is. For SMART, it would essentially mean replacing the current trains, as I don't see much possibilities to convert them at reasonable cost (but I may be wrong on that).

But then, the fuel cell-driven trains are much quieter than the diesel-driven equivalents…