Hi samjco,
You can already push from multiple Source sites to a single Target site. Just configure each Source site to use the Same Target site in the WPSiteSync Configuration settings. WPSiteSync keeps track of which site sync’d the data so there is are no duplicates created. And we also handle all of the domain fixups no matter what the Source site is.
To allow multiple Target sites from a single Source site will require some code changes internally on how the API requests are handled in order to allow for Pushing the Content to multiple Targets. We can add these and make them available in our next update which will be released soon.
The biggest difficulties we can see in implementing this is how to design the UX and how to handle errors. For example, if you’re pushing to three sites and there’s an error on the second site, how do you communicate that back to the user via the UI? And do you keep trying to Push to site #3 or stop on the error for site #2? If there are multiple Targets configured, how do you indication which sites are to be updated during the next Push? There is a lot of UI that would need to be added in order to manage all of these options and clearly indicate success or failure for each Target to the user.
We’d be very happy to work with you on this. If you contact us on our support page at https://serverpress.com/contact/ we can send you code and instructions, as well as discuss the implementation details and UX.