As of today Trenchbroom 2019.1 is released and it has just added
experimental and preliminary Q3 map support
https://github.com/kduske/TrenchBroom/releases/tag/v2019.1which is easily adaptable to use with OA so i've started this thread about it. i'll update this post later.
NOTE THAT THERE ARE NO CURVES/PATCHES AND NO BRUSH PRIMITIVES. Q3map2 will only understand the "Standard" map format from the editor.
Also note: the current release cannot parse OA shaders properly. It will crash on comment blocks. This is being looked into.