This set is missing R3 PgUp, R4 PgDn keys for
65% support. These keys should be added to the base kit based on the popularity of 65% layouts in the community.
Accent-colored R2 Esc is not a strictly necessary key and as such can be removed from the base kit.
Since proper spacekeys are included in the base kit, the usefulness of the second 2.25u Shift is relegated to physical support for 660 layouts, which are quite rare nowadays. Therefore, the second 2.25u Shift should be moved from base to the extensions kit.
As a final note, I don't think that including a full set of macro keys in the extensions kit is a good idea. It bloats the price of the kit while not providing that much extra utility. Consider: a) splitting them out into a separate kit, b) reducing the number of columns down to two (two columns is still useful for covering
ortho boards), or c) dropping them altogether.