[edflsafoiewq]

Nice idea. I tried it, it works really well: https://imgur.com/a/p3l6ABh

A software decoder would be tiny and you can use an existing good BC1 encoder.

[IvanK_net]

Wow, nice! I wrote a BC1 encoder in JS, it is quite simple :) https://github.com/photopea/UTEX.js/blob/master/UTEX.js#L198