I like the 40s support but have to be a kill joy and point out that L->R gradient sets are a bit trickier.
The two most common layouts are 12.75u (aka minivan) and 13u. In non-gradient kits, 3-key 40s gives support for both assuming that people are willing to use 'end' as esc (or have a R1 esc in a R2 row).
For gradients though, you also need to consider the shifts. Both 12.75u and 13u layouts use a 1.75u LEFT shift. The 13u layout then uses a 1.25u RIGHT shift (though I suspect very few people would object to using the 1.25u Fn key in its place).
For full 40s support, you'd need to add a 1.75u shift in the dark blue colour. Then there's the issue of the bottom row. Unlike the other rows, 40% bottom rows are just literally made up on the spot using RNG. 1-3 spacebars, 1-1.75u bottom row keys in random places, knobs, etc. Your calm kit is a fantastic solution, because I don't think that the gradient would ever be feasibly supported with all the dumb options out there. As it stands, I think that most layouts will be okay with the gradient if people are cool using the ISO keys on their bottom row.
But yeah - for the base kit you'd either need to remove the 40s support and shift it to another kit, or add a 5th key (1.75u dark blue shift).
