In my opinion, the more realistic approaches at the moment would be either 1, 2, or (in some extent) 5.
If the WEWCC is going to be used a field hospital, then there's an uncertainty that it will be sanitized and returned to normal by late July. Personally, it would be great to push Otakon back later in the year a la Awesome Con (which I'm, happy will be postponed to December), as my experience riding the Metro to and back to some classes this winter has gotten me comfortable enough to use it for events on the Green Line). However, there's a number of factors that can affect that. Among them:
The dates that the WEWCC will be available;
Not wanting Otakon to compete against Anime USA;
Halloween weekend being out of the question due to AWA;
The planned Olympics theme for this year (which will not work, as the games have now been postponed to next year).
As for the "virtual con" idea, that's going to be a challenge. However, I can think of at least two events that could utilize it.
The industry panels (in particular, Discotek, as they've been having some interesting announcements in the past few Otakons)
The AMV Contest, as I've seen the contests for Anime Detour and Momocon take this route when the cons were cancelled.