@sarna
Basically you have to find a intersection of the Lisps you wish to use. The case can be a bit better for Non-Scheme Lisps like CL & Elisp.
So for RFCs you are basically looking at CL spec or Scheme specs or SRFIs.
Whats the issue with comments? Unless you want to pass the comment to other side... 🤔 But I think this is a great feature that they are non-passing. You can always hack something up with regex-replace, it all depends how the receiving end functions.
The only big incompatibility between Lisps are reader macros, but on the other hand you can transform those objects to a easier form like in Racket hash->list, set->list, etc.