Having read through the 7 pages to date, it seems there is no discernible pattern. Expired and non expired domains hit, all niches, WP and non WP sites, 301 and not 301 boosted sites, blackhat and whitehat.
My own experience is exactly the above, I can find no reason why a bunch of my sites have been hit. Particularly annoying for quality whitehat sites. 1 site was 4 years old, with quality links and content, sitting in top spot for multiple KW's for numerous years, now 90% gone!!!
The only thing I am wondering about is 301 redirects. I would point to this, but I have sites with 301's doing just fine, so no proof to point to.
If anyone has or finds better information, please share.