It's hard to gauge the actual demand for this feature. It looks fairly straightforward. Unfortunately, we're winding down our feature development for SlickEdit 2010, and there won't be time to do anything with it. We'll keep it as a possibility for next year.
In the meantime, it should be fairly easy to set up Tools in the Build menu to call command lines for the Maven targets. Likewise, it should be fairly quick to setup new projects in SlickEdit. For Java, most (all?) of the projects I've done used a single source tree. I didn't separate projects in SlickEdit since they built as a whole.
Can you tell me more about your use of Maven that will help me understand whether this workaround is as easy as I'm saying?