Although RCP, eRCP and RAP provide a step in the right direction they miss a true model for portability among these runtimes. Of course the commonality of APIs and the OSGi component model in these runtimes enables us to port applications among them easily but it is not currently possible to use an application on all of them without the porting effort. My first expactation from the top level runtime project is it can bring these projects close enough so that a common application model, especially for those with a ui, exists among them.
Speaking of the UI, SWT is the UI toolkit for eclipse runtimes. I think this may be a good time to move SWT to the runtimes project. I think such a move can strengthen the collaboration among different SWT flavors(eSWT, RWT) and mark SWT to be a runtime aspect of the eclipse rather than the IDE.