I have taken The EDTF proposals and suggestions from listserv and other discussion and have tried to consolodate them into a single table, at http://www.loc.gov/standards/datetime/features.html
which now attempts to capture all of the features that have at some point been discussed. The table provides a list of features, an example for each feature, and for an "extended" feature (one not supported by ISO 8601) a syntax is proposed.
Comments are solicited. The most useful comments would be challenges, along the lines of "why do we need this feature?" For any challenged feature, if nobody steps up to defend it, it will be removed.