Curious if there are any split keyboards with "overlap", eg, the center of the keyboard is duplicated on both sides

Moonlander has an extra row of keys on the inside for both sides that are mappable

Yeah the handful of times I've tried a split keyboard, I dropped it because of this. Like I use a different hand for the 'y' key if I'm typing my (left index) versus yes (right index).

It's an ergonomic keyboard, not a split keyboard, but I have a Feker Alice 98 (highly recommended!) and it's got two B keys, one on either side of the ergonomic divider. Threw me for a loop when I first saw it. I only use the left one. :)

The filco xacro m10sp is a 60% type board that splits down the middle, with a line of extra keys on each side of the center

Gives each split space bar a bonus U1 key in the middle too