+1
I wanted to implement a plugin for it myself, so I can make a move from joplin, but turns out parser plugins are not supported. It’s a common and straight-forward feature of markdown that has decently well-defined format.
Portability-wise, it is unlikely to cause problems. And we already have callouts/admonitions that from what I’ve seen are implemented differently in every parser. Compared to callouts, deflists are not something to worry about, and they degrade more gracefully to plain text as well.