+1 to Howard's question ... but will say 'yes' ... with a 'but' and a 'depending'.
Do that now with File System repo ... a 'unirepo' which can be seen in multiple instances of Moodle on same physical server. In another context, there is LTi (provider and consumer) which could provide 'repository of courses' (with limitations). In yet another context, one could use one Moodle instance as a private HUB from which multiple authorized Moodles could acquire entire courses to install on their Moodle.
'spirit of sharing', Ken