I do plan to add support for Bing maps in Event Calendar Pro pretty soon. We had google maps for a long time in mojoPortal before we added Bing Maps. I like Bing Maps better myself.
However making a unified abstraction around different map services is a much taller order and not something I intend to try and tackle.
I will implement it in Event Calendar Pro similar as it is currently implemented in the Blog which already supports using either google maps or bing (this was added to the blog only a few versions ago).