In reply to Edd Twilbeck.

Definitely. You can register custom patterns via a custom theme or plugin for clients and just disable the core ones.

Related: I also have an open ticket for an API hook to allow developers to load patterns via an external site too. I think it's possible to do this with a bit of a hacky workaround, but there really should be a dedicated filter hook for it. This solution would be better for serving patterns to multiple clients from one source.