EShell not emitting activate signal
EShell does not emit the activate signal to the primary instance on spawning another instance, while its parent class GtkApplication does so.
This seems to be due to Evolution directly using gtk_main instead of g_application_run, which in turn is responsible to call g_application_activate and emit the signal.
This makes it hard if not impossible for a module to hook onto the launch of an instance (primary or not). Also, the doc is misleading in this respect by not pointing out this behaviour with this inherited signal.