The issue of hyphens in dates and colons in times was raised by several members here, suggesting that only one form, basic (no hyphens or colons) or extended (hyphens and colons included), be prescribed in the dateTime spec. And since we cannot profile out the extended form (for a number of reasons) that would mean profiling out the basic form.
The argument for the basic form is that MARC records use the basic form for both date and dateTime, so if basic form is profiled out then marc records would not conform to the spec, unless they are converted, which is unlikely.
I have consulted with a MARC expert and we conclude that only items 201 and 202 matter - "201: Date - without hyphen" and "202: Date/time - without hyphen/colon". There is no existing data in MARC records for any other item in the spec (we think). So there is no reason to allow both forms, for (for example) "2004-06-(11)?" because there is no data of this form yet.
So we propose that 201 and 202 are legitimate use cases and that both basic and extended forms be allowed, but only for date (yyyymmdd) and dateTime, and in all other cases only the extended form be permitted.