if we ever get a total remake of all the textures in quake 3 arena & team arena that would be a good textures to rely on.
Indeed.
I think every texture is meant to stay in OA.
It just happened some were removed due to some unclear copyright story.
That would be great but in the past I got the following situation: I did a fully textured map and took textures from whole OA texture pool. Next release on loading my map textures were missing. Since on re-applying any texture properties (scale factors, rotation factor and such) are lost you will end up spending much time redoing this. Also you have to spend much time on finding out if the textures are removed or just shifted and IF they got shifted, where they are located now - this time is better spend in improving the map's brushwork and such for sure.
Textures with unclear license or copyright issues should be taken to the dynamic pool since they are not granted to be in the next release.
Besides the removal there are issues.
Lei exchanged several textures by ones with higher resolution that look plain and pretty featureless. Maps like kaos2 and oa_koth1 don't look like they should until the highres ones get replaced by good textures.
This is exactly what I meant by changing. Even if a texture is located at the same position with the same texture name the map might look strange or ugly IF the texture content got manipulated from one release to another. Suddenly perfectly fit textures won't fit anymore. Texture updates of the kind described by you should only be done to textures of dynamic pool or at milestone releases.