One can either go down this path, or follow my suggestion from the description list thread and use ~ name : value or ~ name \n: value instead. Definition/description lists that start with a “value” without a name don’t make a lot of sense, so if you don’t allow those, then it would free the single colon as a marker for div blocks (and remove the need for look-ahead in definition lists).
But i actually like the double colon too. As i said: it has that symetry in it. Probably : vs :: is clear enough for the user, but I’m not sure.