Base Kit
(Attachment Link)
Numpad Kit
(Attachment Link)
R1 End, PgDn can be moved from the base kit to the numpad kit, as those keys are only ever used in layouts with numpads, such as 1800/CP and 96-key. Also, double 1u Ctrl is not useful outside of 40% boards. Therefore, I suggest moving R1 End, PgDn to the numpad kit, and dropping the second 1u Ctrl from the base kit (or moving it to 40s).
In their place, I suggest including R3 PgUp, R4 PgDn for full 65%/75% support, as those keys aren't currently present in any kit. Also, I agree with the previous posters that mod tilde/backspace should be added too.
Alpha Kit
(Attachment Link)
Dark Alpha Kit
(Attachment Link)
I don't think this sort of support will be useful even for 60% users since it still lacks many important keys. It might work, but a more ordinary alpha kit would be cheaper.
Extensions Kit
(Attachment Link)
It might be a good idea to add red arrow keys to the extensions kit since they're not present in base.
Conversely, I don't think you need that many Windows logo keys.