It’s only (potentially) buggy if you’re using it to do ASCII art with background colours. That said, I could just check for font-family: monospace and use that as the trigger to activate the rest of the processing.
The issue is if the client is an actual remote client then it needs to go through the GlkOte protocol. It’s the same reason why I haven’t implemented glk_stylehint_measure.
All fonts can have different metrics, so I am liking this idea of recognising the generic font families and converting them to Parchment’s own styles.