It is a complex feature in my long term vision but not something to expect real soon unless some 3rd party decides to implement it. In the long run I would like to be able to export from any db platform and then import into any other db platform mojoPortal instance.
But, like I said, it will be very challenging to implement it well. It may need to be implemented as an interface that can be implemented on specific features. It would be very difficult to come up with a universal solution that can handle any feature. It will also be challenging to handle version mis-matches like exporting from an older version and importing into a newer one.
If or when I ever do implement a solution for this I will probably make it a paid add on feature.
One strategy that could be used in the mean time, is to backup a full db with all sites and then either write queries to delete all but one site or use a local copy of the site to delete the unwanted sites so that only one remains, then produce another backup and it should have only 1 site.