Internal documents circulated to Apple’s authorised service centres have explained the nature of the membrane in the new MacBook Pro keyboard. As suspected, it is meant to prevent dust and debris from clogging the butterfly key mechanism.
Apple is still not publicly admitting that the upgrades are meant to fix a design flaw with the MBP. With marketing material only talking about the quieter keyboard; a feature that seems more like a side effect of adding the membrane than being anything intentional.
On that note, iFixit has published a more rigorous test of the MBP membrane. Subjecting it to a powered paint additive to simulate dust buildup over time. In this case, the membrane did what it is meant to do and prevented any of the powder from entering the mechanism.
However, the test involving larger particulates (in this case sand) resulted in the keys getting stuck.
The teardown of the MBP also reveals just how difficult it is to actually get to the keyboard to fix it. There are several rivets holding the chassis together, requiring them to be broken before the keyboard can be accessed. In other words, this is no easy replacement job.
Apple is unlikely to ever come out and say that it was trying to fix a problem with the keyboard on the 2017 MBP. Not when people are discovering some newer problems with the MBP 2018.