I think that almost any core-lead 'setting of foundations' is a good idea. The current set up is old, complex and confusing.

Domain mapping is at bursting point, and will end up with either no solution in the public domain, or with lots of insufficient work-arounds that will confuse newcomers even more.

It makes sense for the WordPress Network to support domain mapping out of the box. Who doesn't have a network with sites that want their own URL?