[onetom]

A split space-bar version could make it a lot more versatile, without a lot of drawbacks, imho. You could use the 2 halves as layer keys when held or one as space, the other as backspace, or if one half is pressed, then the other half could mean backspace or enter.

There is also the SpaceFn layout, which works with just one space, I know: https://geekhack.org/index.php?topic=51069.0

but it feels like it could be a lot better with split spaces.

[CarVac]

In my opinion the best use for a second thumb key is Shift, to take load off of the pinky fingers.