Compressible file types have limited value/use
With the addition of libarchive integration and the migration of the temp_xfer section to JS, the compressible file types (configured in SCFG->File Options->Compressible File Types) have very limited use: they really only serve to compress QWK/REP packets that use a non-libarchive-supported type of compression/archival - and nothing else.
Consider either: getting rid of compressible file types or making them a bit more useful by exposing the temp_cmd() function in the JS object model. At least then the compressible file types (or type of user's choice) could conceivably be used by tempxfer.js or some other JS module.