Very interesting.
A few random observations:
1) Are all KAT sets going to go with the "let's forget tertiary legends exist!" thing?. It's natural for US English, forgivable for UK English (omitting ¦ is a good thing to do, while omitting € is not ideal but passable) but... more and more difficult to pull off nicely in every other main national layout (German, all Nordic layouts, French, Spanish (both), Portuguese (both), Iberoamerican, Italian, New Italian... not to say anything about Central and Eastern European layouts).
2a) Seems all KAT sets that choose icons are going with ⌦ for the Delete key (excellent), but that begs for the corresponding ⌫ sign for Backspace. Perhaps this should be an option, given the importance icons are given in this IC.
2b) IMNAAAHO, the icon for Insert (a down arrow) needs revising (looks like a misplace Caps Lock). Also, the icons for Print Screen and Pause seem to be swapped in the render. The Scroll Lock icon is unrecognizable (see below for more on this).
2c) I dig that the Alt icon has been mirrored over for the right side. However... since the 1U Alt key is very frequently placed on the right side, perhaps modifiers kit will need a 1U "mirrored icon" Alt key as well.
3a) Why copy the Cherry-style × and ÷ symbols on the numpad? Those keys produce * and / respectively, not the other symbols.
3b) I dig the Lock icon for Num Lock. But it begs the question... why three rather different "lock" symbols for Caps Lock, Num Lock and Scroll Lock? (the latter in need of a revision, as well) Could a common root icon be used for the three of them?
3c) R0 Esc in the numpad&1800 kit seems to be unnecessary (after all, it's already present in the TKL kit).
4) ISO support: UK English is correct (minus the tertiary legends, blah blah). Please consider adding an R3 \| key to complete support for US English over ISO and ANSISO. Also, I like the icon for AltGr.