Here are some quick examples, using only 256 unique block color/intensity table values for each image, and RGB avg. error metrics. There are actually two tables for each image, one for differential and another for individual mode, each built from the same 256 clusters. The tables are closely related, so it's possible to store the block colors in 555 format and use them as predictors to delta code the 444 block colors.
This is the first (and trickiest) major step to full ETC1 CRN/RDO support in Basis (the successor to crunch). In practice I think 256 unique endpoints is too few, but I'm purposely limited the # of clusters to get a feel for how well the current algorithm works.
kodim18 at 256 endpoint clusters, with tile and differential bit visualizations: