There is no base standard when it comes to kitting, but the one I posted below is generally what the average kitting will look like (except for 1.5 function, that isn't common in base at least)
It really depends on the person, but generally a good set will accommodate all of this at the bare minimum (there are some exceptions, I have seen people remove 6.25u bottom row for smaller runs with sp for example)
For extension kits, you generally see stuff like mx hhkb support, r3 and r4 pg dn and up, shinethrough caps that sorta thing. But again that varies among designer, If I ever run a keyset mx hhkb support will probably be in base.
Thanks. My issue is always finding wider keys from sculpted profiles outside their normal rows. Even as blanks, that's not easy, though it certainly looks like I might have some options with R3 1.75u and R2 1.5u. I am noodling around with one more hand-wire project before I start exploring PCB design. I haven't quite figured out what it'll be, but accommodating sculpted keycaps is something I'd like to include.