There'll be demand for the new MMs once they get finished, I'm sure of this, even at 12K.

There are a lot of negativity towards Wayne on rgp and here - but most of the pinball world is not aware of all this history. When new MMs become really for sale (on his website or on ebay), people just see that this great machine is for sale in NIB condition. That's what'll matter to them.

As for collectability and value, imo MM is different from BBB.
BBB got hyped because it never ran in production and it was rare, only 10 (or 12 or whatever..) produced. Even the re-run was very limited, less than 200, you had to enter in advance, ..
Most of its value is just because its rare. Original or repro matters more because of this.

MM on the other hand is just the greatest, best playing game ever made If WMS hadn't stopped making them, they might have have sold more of them than they did of TAF. It's just a game that everyone loves, and demand is very strong, even from non-pinball collectors.
It's value is mostly not because it's an extremely rare game, but because its a great game to play.
Therefor imo 'Bally MMs' will also be in demand.