Maybe if the head of engineering had had another 6 months to test the keyboard design properly he could have concluded that it wasn't technically feasible. But at the time there was a lot of pressure to release a redesign of the MBP and probably the design of the case was already decided. In the end Apple wasn't able to make a proper keyboard to accommodate the specs but maybe it was too late to go back to the drawing board.
I'm speculating of course, but I very much doubt Apple are complete idiots. It's more probable that some circumstances forced them to release the redesign. It was a mistake of course, they should have only updated the specs of the 2015 model, maybe adding a TB3 port. But you know, hindsight is 20/20.
I imagine Apple has been working on a redesign with a new keyboard, but these things take a couple of years. Specially when the Mac is only 10% of Apple's revenue.