Interesting concept. I have two comments, one objective and one strictly subjective:
1) ISO support has one minor error that can be easily corrected. In the base kit as it stand now, you have: mod-colored 1.25U left Shift (good), mod-colored ISO Enter (good), accent-colored ISO Enter (great), R4 \| (good) and R3 #~ (OOPS!). With this, you are giving full support to neither US ISO (the R3 #~ should be R3 \| instead), nor to UK ISO (the remaining four alpha keys, R1 `¬, R1 2", R1 3£ and R3 '@ are missing), but are falling into the "middle of the pond", which is the worst option.
I would suggest the simplest solution: support US ISO by replacing the R3 #~ with an R3 \| key in the base kit. If UK support is asked, it should go to a separate international kit (NORDEUK being the typical option).
2) This is strictly subjective: I find the legends on the alphas to be difficult to read; perhaps using the accent-color for them would be an improvement (but WDIKAA).