Let me first point out that I am in the process of wrapping up Maps (and Semantic Maps) for their 2.0 release. These will include the new features Kim added, amongst which the Special:MapEditor page using Google Maps. This means that any additions you make will be for a release after 2.0 (which might not matter much to you as you can happily run the latest version of your own code or the extension itself).
Adding another editor using OpenLayers would be awesome. There are however two points that when taken into account will make it even more fantastic:
* Having different editing tools for different mapping services is awkward, it's nicer to have one interface that can just switch mapping service (much like the existing (non-editing) interfaces).
* The editor Kim created can eat and output wikitext. This allows users to get the wikitext they need to embed a map without actually understanding it or having to write it all out. They do need to actually navigate to another page, so the UX here has lot's of room for improvement. A kind of inline editor would be amazing.
Jeroen De Dauw
Don't panic. Don't be evil.