One of the main reasons why I'm sometimes switching to other IDEs for some projects is that they allow me to have multiple projects open at once. I know IDEA allows you to open multiple projects in two frames but I usually need something more structural.
It is mostly about the ability to work in two projects at the same time and then run the two projects 'as one'. Many of my projects have dependencies on eachother and right now I have to switch to project A, build and install it and then switch bakc to project B which will reload those jars. Which is kind of a pain.
I know it is possible to hack around this by simply creating a project that includes the source of both but in many cases that is not very practical.
Not sure if the feature roadmap of Selena has been defined and closed already but I'm sure many people would really enjoy a feature like this.