You can't really put the C-141 into the same bracket as the Diesel 8 though, the Lockheed would give that low floor and odd size ability that the Douglas would lack. It's that odd/outsize work that would be the same justification for the BC-17. When the C-141 was being built, there wasn't the same profile of work which exists today (AOG large turbofans for one).
However it does point to the lack of speciality work generally which put an airframer off offering it.
Maybe the proposed buyers have some cast iron contracts in the bag to fund the fleet. Who knows. Something got a capital firm to make a LOI deal on financing it. Could Boeing be offering shipping contracts as part of the purchase deal?
There are going to be a lot of Trents shipped to Seattle in the future...and GENx units flown the opposite way to Tolouse. Add in oil industry work and other odd size freight and I suppose it could be made to balance.
Mere idle speculation naturally...