I like proposal and please, invest time to to ensure good compatibility with libevent-2 main loop and consider even its buffer events. I think that that library is good candidate for generic mainloop for most of applications.
But there is need to live with GLIB based mainloop as well. Its interface is so rigid and unfortunate that only option for other GUI systems (like Qt) was to switch to GLIB mainloop when GLIB based loop libraries are considered for them. I hope that GLIB community would invest time to that problem some day but it cannot be done without API level compatibility break.
You can look at my ul_evpoll effort as a source for some ideas too. It started in libevent-1 days as an solution to write libraries requiring system level events registration and compatibility with GLIB and yet to be able to switch to libevent. Then the project little extended to provide own implementation of select, poll, epoll and winevent mechanism and ability to plug-in into GLIB, libevent-1 and libevent-2 based applications.