See here for one working open-source implementation.
As understood, it is planned to release "official" open-source backend as well:
In fact, in the near future, even the above trade-off will be eliminated as we're presently working to open-source a version of the back-end, which anybody can run as their own server at home.
There's a plan for some back-end overhaul as well:
In progress by vtnerd Complete overhaul of back-end, and replacement of polling with sweet push-based synchronization (Issue #46)
So yeah, the plan is to let everyone run their own back-end, as indicated here. Quoting fluffypony:
He's done excellent, excellent work - we've spent months on this, and hopefully it'll make MyMonero a significantly safer service to use, especially when you use it with your own node.