Hi,
No it is far from obvious which approach, i.e. separate UML-RT specific menus or having filtered version of some common menu, is best from a user experience point of view. We have had this discussion not only regarding the new diagrams menu, but also for the new relationship menu (where
bug 507277 proposes to have a separate UML-RT specific menu, but we currently create generalizations using the "ordinary" UML menu).
I see this as highly related also to the principle of a separate and customized UML-RT tab in the properties view, vs. the ordinary standard UML one (which we do not customize/filter at all). There we have discussed to configure it so that the UML tab is not shown at all, for the minimal, pure, UML-RT experience. But for the advanced user, or the scenario where UML-RT is mixed with ordinary UML modeling, you can have both tabs.
The legacy tooling have really not had any specific UML-RT menus, or tabs in the properties view, but have "blended" things in with ordinary UML modeling. Personally I like the style that we started using in Papyrus-RT better, i.e. a separate UML-RT new child menu and a completely separate UML-RT tab in the properties view. But still I don't know which one of these two approaches gives the best overall user experience, for all the different scenarios we can see and different configurations of Papyrus-RT, from the "miminal" Papyrus-RT configuration to combining UML-RT with base UML or possibly other DSMLs.
/Peter Cigéhn