Omega Keyboard is missing two keys to be JIS layout.

[dude22072]

On JIS keyboards, both MSX and modern day, there are two extra keys compared to US QWERTY layout that are missing from the Omega Keyboard.
JIS Keyboards have three keys between L and Return, whereas US keyboards only have two.
Similarly there is an extra key between /? and right-shift, making a total of 4 keys between M and Shift.
Technically speaking the spacebar is also shorter to make room for 実行 and 取消 keys, but very few MSXes have these keys. They seem to only have been included on models that were marketed as word processors.
Since the Omega Mainboard has a jumper for JIS keyboard layout, I think the keyboard PCB should be updated to include these two extra keys.

[skiselev]

How important are these keys? Is there any software that doesn't work without them?

Looks like it will require decoding all 4 rows (instead of just 3 in Omega keyboard).
It is doable. But will require keyboard redesign, perhaps similar to this: https://github.com/vipoo/yellow-msx-series-for-rc2014/blob/main/keyboard/schematic.png
Keyboard JIS keyboard matrix, for my own reference: https://www.msx.org/wiki/Keyboard_Matrices#JIS_Matrix