Everything is possible as you know BUT don't forget that the SDL plugin is 100% end-user oriented.
The end-user wants to know one thing: a URL+port, a language pair.
If we put too much settings in the plugin, it won't be usable by anyone (end-user or IT guys @end-user)
A multi-lingual REST layer is needed in my view.
We have started one, along with the SDL plugin, which communicate with the ModernMT back end.
I think there an added-value to be compatible with some other existing systems.
Only issue I see, it may really overlap with some stuff taht the Systran folks do on their end.