I have just a practical explanation why ?/? and other options you listed below should not be allowed.
To me, in the context of ISO 8601, an interval which is open at both ends is not meaningful. Either the end or the beginning of interval has to be specified since the meaning of ?/?, "/" and all the other intervals with unspecified or unknown beginning and end could be understood to mean eternity. Which is different from e.g. the age of the universe; that could be specified as an open ended interval starting from big bang about 13.798 billion years ago.
We may of course assume that there is a platonic world of philosophical and other ideas out there, so when someone in India invented zero he/she just brought down to us something that has been there waiting for us out there even before the big bang. But I would not use this approach with ISO 8601. I'd rather specify an open ended interval starting from the first known or estimated occurrence of zero in surviving documents (I guess this is the librarian's approach to implementing ISO 8601 :-)).
One problem with encoding the age of ideas with ISO 8601 is that you would need to decide what belongs to the world of ideas and what was invented by us. Or, as German mathematician Leopold Kronecker put it, "God made the integers, all else is the work of man".
> -----Original Message-----
> From: Discussion of the Developing Date/Time Standards
> [mailto:[log in to unmask]] On Behalf Of Saašha Metsärantala
> Sent: 29. heinäkuuta 2015 16:18
> To: [log in to unmask]
> Subject: Re: Open-end interval
> Thanks for all those interesting suggestions!
> As I understand our situation, the aim of our focus shift from EDTF to ISO-
> 8601-2 is not only a way to try to give this standard deeper roots but also a
> shift from a focus on date representations within the library / archive
> "culture" to a wider world of digital representation of date-time information.
> Keeping this in mind, I consider that we would need a deeper explanation to
> clarify why "unknown at both ends"
> > a construct like ?/? would be explicitly forbidden (as would "/" for open at
> both ends).
> This wider world may include, for example, philosophical ideas. Let's consider
> a "software" (or schema or some future something ...) requiring date
> information for (philosophical / ideological) assertions. How would we date
> the assertion / belief that
> "1 + 1 = 2"
> (assuming that the characters within this assertion keep today's meaning)?
> Other examples are welcome, of course. In other words, I suggest to clarify
> EITHER what "/" and "?/?" (as well as "/?" and "?/") would mean and in which
> cases these may be useful (in a wider perspective) OR more exactly why we
> choose to reject them.