Re-replying back to my question. The original message didn't seem to get a lot of traction when I posted it. I have posted a Phabricator patch here (⚙ D94250 [SystemZ] Introducing assembler dialects for the Z backend) which details a bit of what I spoke about in the original message (i.e. providing a custom overridden implementation in SystemZAsmParser.cpp to return the MAI's assembler dialect and provided a comment as to why it is problematic to query the overridden getAssemblerDialect function in AsmParser).
If there are any objections to this please do let me know. Alternatively, if there's a much nicer/cleaner way of going about it, please do let me know as well.
Thanks and Best Regards,