When I got the idea to implement system connections I thought in just fixing a bug, but since NetworkManager is changing its API and ABI during the 0.8 to 0.9 transition the challenge has increased.
The main change from 0.8 to 0.9 specification is that now all connections are system wide with new DBus interfaces for the clients (Plasma NM for instance) to provide secrets (user name, password, encrpyt keys) to NetworkManager. Most of the changes are there to shrink NM's clients (Plasma NM, nm-applet, cnetworkmanager) source code, so it seems to be good change. We will need to change Solid's NM backend to meet the new specificaton, which can be problematic for distributions because they will only be available in KDE SC 4.7, scheduled to be released in late July.
Talking about distributions, one Fedora guy showed up in kde-networkmanagement mailinglist. NM-0.9 is going to be released next week and Fedora guys are thinking in using NM-0.9 in F15, preferably with a working Plasma NM. To do so would require changes in KDE SC 4.6x API used in F15, something that KDE tries really hard to avoid.
One good news is that a guy from Pardus Linux (Gökçen Eraslan) have been working in implementing system connections since last year, I just forgot about that hehe, sorry. So we already have a working implementation but Gökçen Eraslan still have not answered my e-mail about his implemenation. If it is working good with no side-effects we can add it to networkmanagement master repository and starting from there to meet NM 0.9 specification from Plasma NM's point of view. The Solid's NM backend part will need more discussing about how to proceed.