There actually has been a fix already tested. It didn’t work, so they’re looking for another fix. I’ll check for where I saw the post–I believe it was one of Leviathan’s. If I find it, I’ll edit this message to include a link.
EDIT: Referenced link is When are the US Servers Coming Back Up? - #2 by Leviathan-1945
For the benefit of easy viewing, here’s the content of the referenced post, slightly edited for relevance:
As for ETA’s Bliz typically doesn’t give them. For example, they have already tried a fix which didn’t work. Had they given an ETA for that, it would have been for nothing. The vast majority of the time they announce a potential fix at the moment it’s released.
There have also been reports of a workaround that has worked for a few people. For me, personally, this did not work, but Juicy said it worked for them.
I did see one community post stating that tabbing out during the authentication screen helped them.