Wait, is the set missing an R4 1.75u Shift key? There seems to be two extra Shift keys in the base kit which I'm unable to determine the width of, are they both supposed to be 2u, or is one 2u and the other 2.25u? It's hard to tell from the renders.
But you should replace at least one with a 1.75u.
EDIT: Actually you might want to keep 3 you have provided they are 2u+2.25u and just add a 1.75u one. Yes, 4 Shifts for R4. But I do believe 1.75u is more important than some of the others. I can't quite remember though.
Also is the set missing an R3 \| key or am I blind? I see there's R4, but not R3.
And I have to say; one thing that's really, really missing is an R3 1.75u novelty for Caps Lock/Control. As I see it, there are three options;
1. Include R3 1.75u novelty key with a drawing in the novelty kit
2. Include R3 1.75u red + R3 2.25u (and perhaps ISO enter) red with text like Esc key in any kit, with text like "What about lunch?", or "There is no hurry" for example (it can't just be one extra red key for the R3 caps/ctrl because then the board would be completely unbalanced when it was used - needs a red for the right side as well then)
3. Include R3 1.75u novelty key with a drawing in the base kit, which is large enough already