It does make sense to specify the action language at a higher level. My main concern is how to link other languages with the "core" UML-RT Xtext grammar, in such a way that we can keep the action language(s) separate. Right now I don't have an answer to that. I'll keep investigating.
We realized that there is another important issue: should the textual syntax support the concepts from the RtCppProperties profile? If we are to support it, the question is how. How should the textual syntax for that look like? Also, since it is a C++-centric profile, I think it should be kept separate from the core grammar.
I also have another (simpler) question: the suggestion for five keywords for ports, is, I assume, to replace "notification", "published", "wired" with something like "external port", "internal port", "relay port", "sap" and "spp"?
By the way, one of the improvements is already merged, in case you didn't noticed it:
62275. The 'entities', 'protocols', 'packages' or
'typedefinitions' groupings in a model or inside a package have been removed. You can directly write capsules, classes, protocols, packages and typedefs in a model or inside a package and in any order. Keep in mind that content-assist is not yet aware of qualified names, so it is currently possible to access only names within the same namespace (package).
I'm still working on the other improvements.