This is a fantastic development, and no mistake. That needs to be said first.
In discussions about Markdown implementation on Meta.StackExchange (of various kinds) some of the most desired features not implemented in Markdown have been identified: support for tables and footnotes appearing high in the pecking order, but definition lists and even “special attributes” might be added (this latter not nearly so significant, imo, but still worth noting).
These of course have long been found in MarkdownExtra and it seems inevitable that the question should be raised about where these fit in to the Standard Markdown initiative now that it has seen light of day.
So – what plans for implementing these “extensions”, then?