What I would like to see from NetworkManager is the ability to support, in some manner, the ability to have bridged interfaces, macvlans, or other type of those sorts of things.
Right now the best approach is to throw your scripts to do the admin-y type odd network configurations using the NetworkManager dispatcher. This in itself is not a terrible thing and is actually very useful... but...
What I've noticed is that while examining virtualization management solutions (ovirt or openstack type things) is that nobody actually knows anything about networkmanager or how to use it properly. If the something like that mentions network manager at all they say something along the lines of: 'turn it off as it is known to cause issues for some users'.
So what you end up with is each solution you run into has their own half-baked way to set up bridges and other things. I think that adding bridging support will go along way towards helping people kick 'must make custom scripts' syndrom when setting up rather mundane configurations.
Especially for Fedora.. the quicker they can get away from using ifup/ifcfg scripts and moving to using nmcli/keyfiles the better off it'll be.