ben_thatmustbemecorrect, micropub assumes your site has only one endpoint. That said there is nothing stopping your site from doing whatever it wants with the data it receives, including passing it to other micropub endoints
ben_thatmustbemei could see someone making a service quite easily that just gives you a unique micropub endpoint and then lets you add as many target endpoints as you want and set a few simple rules to decide what data goes where
ben_thatmustbemecould even write the rules to allow sending a post with category X to send to multiple sites. Which i think might be a great way for me to post photos of my daughters to their own websites as well as mine.... hmmm