Change:
follows: Each PSK SHOULD be derived from at least 128 bits of entropy, MUST <del> be at least 128 bits long, and SHOULD be combined with a DH exchange, e.g., by using the "psk_dhe_ke" Pre-Shared Key Exchange Mode in TLS 1.3, for forward secrecy.  As discussed in sec- properties, low entropy PSKs, i.e., those derived from less than 128 bits of entropy, are subject to attack and SHOULD be avoided. If only low-entropy keys are available, then key establishment mechanisms such as Password Authenticated Key Exchange (PAKE) that mitigate the risk of offline dictionary attacks SHOULD be employed.  Note that no such mechanisms have yet been standardised, and further that these mechanisms will not </del> <ins> be at least 128 bits long, and SHOULD be combined with an ephemeral key exchange exchange, e.g., by using the "psk_dhe_ke" Pre-Shared Key Exchange Mode in TLS 1.3, for forward secrecy.  As discussed in sec-properties, low entropy PSKs, i.e., those derived from less than 128 bits of entropy, are subject to attack and SHOULD be avoided.  If only low-entropy keys are available, then key establishment mechanisms such as Password Authenticated Key Exchange (PAKE) that mitigate the risk of offline dictionary attacks SHOULD be employed.  Note that no such mechanisms have yet been standardised, and further that these mechanisms will not </ins> necessarily follow the same architecture as the process for incorporating external PSKs described in I-D.ietf-tls-external- psk-importer.

Discussion:
NIT: Might be better to say: Just drops some redundant words.
I think some things that should be more positive: -- For both PSK authentication and PSK key exchange without (EC)DHE the bad security properties such as lack of identity protection and lack of forward secrecy can be overcome by using one-time PSKs. External PSKs with short lifetimes are quite common in many real deployments. I think this should be mentioned. -- I think quantum resistance should be mentioned earlier in the document. Quantum resistance is a security property, not use a use case. Some things that should be more negative: -- In the list in 4.1 you can add "4. Any group member can blame any other group member." Other comments: -- "then PSK-only key establishment modes are secure against both active and passive attack." I think this you need to describe the exact attacks you have in mind rather than use the work "secure". My view would be that acceptable security in 2021 includes both identity protection and forward secrecy. But more on a system level, then necessarily by TLS itself. -- "DH" I think it would be good to change all “DH” to “DHE” and all “Diffie-Hellman” to “ephemeral Diffie-Hellman” to avoid confusion with the static DH cipher suites in obsolete versions of TLS. -- "As discussed in Section 6, there are use cases where it is desirable for multiple clients or multiple servers to share a PSK." "However, as discussed in Section 6, there are application scenarios that may rely on sharing the same PSK among multiple nodes." Unless you have any real deployments to share, I think this should be reformulated. These are Gedankenexperiments used to illustrate the attack, not real-world applications. I would reformulate and remove "desirable", group PSKs should be very much discouraged. Suggestion: "As discussed in Section 6, to illustrate their attack, [Akhmetzyanova] describes scenarios where multiple clients or multiple servers share a PSK."