Negative Space 留白: the spacebars kit
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Includes non-traditional spacebars and spacekeys, as well as variant WS1 bars for a distinctive touch.
I'm not sure that the inclusion of white 3u and 2u spacekeys is a necessity. Users would probably get more mileage out of a second black 3u space (for split 3u+3u or 3u+1u+3u setups), and the white 2u space can probably be removed outright seeing as ortho support in base is incomplete, and there is already a black 2u space in the kit.
On a separate note, you can probably remove the second R4 1u Ctrl key and R1 1u Backspace from the base kit.
Two 1u Ctrl keys are not used on any modern ≥60% boards, only ortho 40%. I believe users (especially in China) would get a lot more mileage out of a R4 1u Shift key, which (together with 2u Shift) is used by the GK64 and similar 60% layouts with arrows, which are very popular in the East.
As for 1u Backspace, not very many boards at all use this size. A notable one is Minila, but this set lacks a couple of keys to be able to support that layout (R4 1.75u Control, R4 1u Shift, among others).