I am slowly working on prototype. The work is simple, when variables are just scalars. But it is much harder, when we allow composite variables. When prototype will be done, I invite any cooperation - there are lot of question - and one very hard - where and how the variable should be stored (values) - now I have workaround, but it is pretty ugly code.
I'm not a big expert on postgres internals, but ready to participate.
big thanks. I'll start new thread to stop do offtopic in this place.