Custom `loop_factory` for `asyncio`

[NicolasT]

Hello,

I have a use-case where we'd like to run the ipykernel main-loop using a specific asyncio.AbstractEventLoop implementation (not the stdlib's default one). Since in the main branch of ipykernel the code was migrated to use anyio, I believe this boils down to passing a suitable loop_factory value in the backend_options passed to anyio.run (unless Trio mode is enabled, of course).

Would there be any interest in a patch to allow this, essentially adding a --IPKernelApp.asyncio_loop_factory config option (a DottedObjectName)?

Thanks!