Blender editing & .fbx-exporting UV's all 4 channels rather than just 2 per texcoord

Hi dear fellow TAs !
As far as I know, Blender considers “UV channels” as storing only 2 floats values (U and V) and Blender’s .fbx export feature writes only 2 floats per texcoord to the file (making == 0, if I’m correct). Whereas realtime application’s shading & rendering APIs (directX and openGL) support usually 4 channels per texcoord.
Also, blender seems to not support nor export Alpha channel for vertex color.
I know blender is sometime used in video game production. How do you address this limitation ?

I could consider patching texcoords 2 by 2 at mesh’s import time in the engine I use (Unity, right now), or maybe making a PR for blender’s .fbx exporter. But maybe a solution exists already ?