I'm the assigned ART reviewer for this document. While I'm aware of TZ and its use, I have no competency in this technology. 

Comment 1)
quoting Sec 3.2 time zone designations: "The character encoding of time zone designation strings is not specified; however, see Section 4 of this document."

quoting Section 4.: "Time zone designations SHOULD consist of at least three (3) and no more than six (6) ASCII characters from the set of alphanumerics, '-', and '+'. This is for compatibility with POSIX requirements for time zone abbreviations."

I think this text shall be improved, as the 3.2 text says no encoding specified, while section 4 defines clearly a character encoding that is the current usage. Moreover, it should use MUST since nothing is described for implementations that would not follow if they are pretending the SHOULD. Suggesting to merge the text of section 4 into Section 3.2 and remove the Section 4 bullet point and use MUST instead of SHOULD. 

Moreover, especially given that modern programming languages default charset for Strings are often UTF-8, and given internationalization requirements in IETF, a paragraph discussing the rationale of not using UTF-8 in this version or in the future might be worth.

Comment 2)
quoting Sec 4. Interoperability Considerations: ""application/tzif-leap" (Section 8.2) to indicate that leap-second records are included in the TZif data "

In IANA Considerations section (8), the description for application/tzif-leap and application/tzif are identical, which does not help a viewer of the IANA registry to decide which one to use. Suggesting to add text in 8.2 "Applications that use this media type" for application/tzif-leap to the fact that this one includes leap-second records so that the IANA registry do contain a differentiation text.