I believe Gitlab and Github both render Org files with OrgRuby[1], which is MIT.
Why can't you make a GPL plugin for whatever editor you use?
Re:Org-mode parser in Rust
by Lord_Nightmare on Tuesday April 16, 2019 @02:29AM
(#19671562)
It depends on whether it is an essential dll or an optional plugin. I probably could have phrased that better originally.
Hence, someone would have to properly clean-room reverse-engineer org-mode in order to achieve 100% compatibility, or make a somewhat-incompatible implementation based on the reference docs instead.
As I understand it, Markdown has significant limitations which org-mode doesn't have, but is under a 3BSD-style license. (It also has issues of x+1 slightly incompatible implementations)