I'm tagging NM back to fb7b08388e9de5440962337e20a823bbf9d019ae in Continuous.  Previous discussion:

<walters> [10:48:47] hi, recently NM stopped being able to create default wired connections if there's no distro plugins; I see (eth0): couldn't create default wired connection: No plugin supported adding this connection
<walters> [10:48:50] (in Continuous)
<walters> [10:50:40] i thought the keyfile plugin was built-in
<dcbw1> [10:55:11] walters: yeah, that's odd
<dcbw1> [10:56:21] walters: do you see "Loaded plugin keyfile: (c) 2007 - 2013 Red Hat, Inc.  To report bugs please use the NetworkManager mailing list." in the logs?
<walters> [10:56:42] yep
<walters> [10:57:04] maybe this is beb18050b5a00a704a74bff5c10919b44f087122 ?
<dcbw1> [10:57:54] walters: I think it's likely fallout from the libnm gdbus merge
<dcbw1> [10:58:21] or could be that, but I"d suspect not