As a reminder, Ubuntu MATE’s Martin Wimpress has announced that Ubuntu MATE 15.10 will not come with any software center installed by default and will permit the users to choose the one they prefer, between the Ubuntu Software Center and App Grid.
The Ubuntu Software Center is the software that permits the users to manage the repositories and install the applications via the default repos or the repos that have been added.
The Ubuntu Software Center has not been updated in years, but some Canonical developer proposed in the mailing lists to port the GNOME Software Center instead. But this is just a proposal and nothing has been settled yet.
The other two scenarios are to improve the USC and port it to Python 3, or to ignore it until the Ubuntu Touch software center becomes usable on the desktop.
If you ask me, Canonical will ignore the problem and adopt the Ubuntu Touch SC when it will be ready.