I daily-drove an IBM Model M that was a few months older than me, for about a summer. I love it, but it's just so comically oversized for my desk, even while using a deskpad.
Modern custom mech boards, like my current TKL, allow for extra function layers. You can hypothetically set up a 'numpad layer' on '890', 'iop', kl;', actuated by a layer key that can be held with a finger on the left side of the board. Less overall movement of one's fingers and arms, with equal access to the numpad functionality, if one needs it.
If you want a proof of that concept, see the Planck. Hypothetically, this little thing could replace your desired 'Space Cadet' or 'Battlestation' style keyboard with less than 50 buttons: https://olkb.com/collections/planck
