1) The responsibility lies with Evernote to keep up with Apple. This is what the Sierra beta process is for. If they can't keep up, they shouldn't be in the software business, or at least in this part of the software business.
2) "Your understanding" is totally unhelpful to us. What we all need are results, and Evernote would do well to provide official updates on this forum. You've already commented this is a "user forum" but it is also an Evernote hosted forum and "customer service" is location agnostic.
Evernote is lucky in that it seems their users are both very patient and without many other options, but the length of time it is taking to resolve the issue and lack of communication (besides hearsay) is getting old.