Is it possible to allow people to submit their own events to CiviCRM?
I am not going to be able to discuss a full recipe here :-) But yes, I would think it is feasible and I would certainly use Webform for this. I could imagine a situation where you have one Drupal frontend feeding into more CiviCRM installs, where each organisation would have its own CiviCRM database? If the organisations do not need to share any contacts that might in fact be the easied solution? You keep track of the organizations in either Drupal or a CiviCRM install, with the settings that their CiviCRM installation requires? Interesting project!