RS> FidoNet is a legacy protocol that must (from what I've observed) RS> be enhanced only in backwards-compatible means.
Could you please cite any backwards-compatible enhancement to the packed msg format that has happened since 1995. Kludges don't count since they aren't part of the packed msg format, up to and including dubious MSGIDs.
RS> And if you're going to introduce another date/time format, best RS> to use existing standards (e.g. RFC822 or ISO-8601) rather than RS> introducing yet another date/time format.
That could easily happen. Here is an ISO-8601 version of the RFC-3339 datetime stamp at the top of my reply; 2021-03-31T06:22:08,863177505+00:00
I haven't read the document in a number of years now but I seem to recall that an acceptable format can use the ascii space to replace the 'T' which yields the RFC-3339 version exactly.
If it is the nanoseconds you're objecting to (citing c89 compatibilty) then "2021-03-31 06:22:08+00:00" would work just fine and thus live up to your above posted "be enhanced only in backwards-compatible means". However that will still break abandonware, which never really had any legitimate claim to backwards compatibilty in the first place, including the 1995 packed msg format still in use today.
In other words, I am calling BS on the backwards compatibilty arguement. You got nothing in that direction.