UV printing finally getting the attention it deserves. Marvelous execution, too; and a catchy, meaningful name to tie it all together. Good job all around, Nathan.
As you mentioned, there currently aren't enough R4 1u keys for ortho support. You could move one of the R3 1u keys to R4 (I don't think you need three of them on R3). You could also technically move the R2 decoration/column key to R4 if you make some adjustments to the R3 keys' icons, but I don't think that's necessary. So you would just need to add one extra R4 1u key for complete ortho coverage, if I'm not mistaken. (In which case it'd even be
technically supported with just the base kit due to the 2u numpad
0.)
Also, this R1 key:
can probably be dropped since the PrtSc/Scroll/Pause keys already cover for it in all use cases, as far as I can tell.
Edit: I'm gonna play devil's advocate and say that if you add a 2u Shift (which I know you hate), along with implementing the R4 1u suggestions from above, you'll be able to say that your base kit officially fully covers all common 40s, ortho
and 60% layouts out there