Would you consider adding just 2 R4 1.5u and 2 R2 1.5u keys to the ergo set? that would actually give the kit some lightweight boardwalk/ergodox support as well as non-ortho 40s support for some of the more adventorous layouts.
legends could be R2 shift, enter and r4 esc, delete or blank.
Edit: i think those keycaps in standard cherry colors could be a buying incentive for people who already own a base kit in similar colors