you cannot have Gnome2 and Gnome3 components installed on the same system at the same time (without a real mess). Its not hard to make Gnome2 and Gnome3 parallel installable, Mate managed just by changing the names. Just like its possible to have GTK2 and GTK3 installed at the same time, or gstreamer 0.10 and 1.0. I am fairly sure KDE3 and KDE4 could be installed together.
If the Gnome devs had bumped the names, or libraries version, or however everyone else does it, then the distros would have been free to offer GNOME3 and keep GNOME2 alongside.
whether the gnome devs made a concious effort to prevent this. or just never got around to making the parallel install work, is a difficult question.
The part you don't seem to be grasping here is that Gnome 2 is no longer supported. It would have made absolutely zero sense for the Gnome devs to go to the trouble of renaming half of Gnome 2 so that it could be installed alongside 3, when they had no intention of further developing or supporting that codebase. Did they rename things at the final release of Gnome v1 so that users could keep on running unsupported code next to Gnome v2? No, and it's not reasonable to expect that they should have done it at v3.
The "Control Center" is updated? I didn't even know there was a control center.
I've checked what I'm running, it's mate 1.2.0, found the cotrol center by using tab completion under the terminal. Well, I find it useless, copying the way it's shown in Windows 7 is a bad idea - items should be alphabetically sorted the right way, top to bottom first then left to right, not left to right then top to bottom. This hurts the eyes.
mateconf disappears? Is there a replacement, text config files or something?
I know I used mateconf-editor to configure a few things, especially of interest there's desktop/mate/session/required_components, where you can change the window manager and fail to change the file manager.
I'm running a hybrid, with Mate, xfwm4 and Nemo that I launch from shortcuts (and leftover things from installing Cinnamon and LXDE, so I have duplicate entries in Preferences, two screensavers that fight each other and trigger in the middle of playing video, lol)
I would like a way of not displaying "Places" in "Applications Places System". Other than that I'm really happy with Mate, though with the new Ubuntu support policy I guess I need to wait till Linux Mint 17 (Ubuntu 14.04) to have a really great new Mate distro with new features and stuff. (Installing stuff on a computer you don't own and leaving it alone for years is nice)