Here's kodim14 using only 256 unique selector vectors and 256 block colors/intensity table indices:
This is just a bare minimum prototype. It doesn't support crunch-style macroblock tiling, or required things like mipmaps, texture arrays, etc. It's a proof of principle prototype that crunch-style RDO compression is totally doable in the full ETC1 format.
Here are more examples. I have PSNR and SSIM stats, which I'm going to focus on next.
512 block color, 3072 selector clusters: