Hi Fabrizio,
I think you have two strategies:
1. Build the importer in VA and export MSE
This is way we are dealing with VW: use the importer in VW and export the MSE file. This was because we already had the importer and FAMIX in VW.
2. Build a dedicated Parser and importer
As you suggested, you could build a parser. I guess that the syntax is not (much) different. In this case, I would build a surrounding parser that deals with the specifics of the .st file and uses PPSmalltalkParser for the actual method parsing.
Given that the Pharo importer already uses the RB AST, perhaps you can directly make the parser to instantiate RB AST nodes.
I would rather favor the second option. If we go in this direction, we could also make it so that the Smalltalk importing infrastructure is flexible enough to only require different parsers.
Cheers,
Doru