Mavis is 44HP, a Mother is 60HP, so together you get 104HP with the jack fields next to each other. Moog have 104HP cases and also provide rails to extend their 60HP rack to 104HP. My main gripe (so far) with Mavis is the lack of USB as a power source so it's not really portable, which makes the case cover kind of redundant. And also makes firmware updates problematic - though there may be a way to attach something directly to the board (perhaps something like the Silicon Labs USB flash debugger).
I guess the design could have been done with the jack field being a separate component which could have been attached via a ribbon cable at either end of the case, so you could position it left or right.