Are the MUST/MAY/SHOULD keywords intended to be interpreted according to https://www.ietf.org/rfc/rfc2119.txt? If so, this should be explicitly stated in the document. If not, the intended meanings MUST be defined in the document or a prominantly linked definition document.
Topic on Talk:Wikimedia Engineering Architecture Principles
Ideally yes, but see my comment about the interpretation of MUST in the "More MUST, less SHOULD" thread.