would an electric sustainer be practical

In a year or three we will know the answer: Schempp-Hirth will be
offering the Arcus as an electrical self launcher with the engine from
Lange and DG will be offering the DG1000 as an electric sustainer. As
both factories are also offering those same gliders as pure gliders and
with combustion engines, we will be able to compare how it all calculates.

I suspect that the certification requirements are probably harder for
self launchers than for sustainers, which will also contribute to the
equation.