Lead Encounter Designer Ion "Watcher" Hazzikostas has taken to the forums to reassure players on post-squish soloing. Despite Blizzard's repeated assertions that the squish will do nothing to affect soloing, the message is going unheard by many, so Ion has provided some clarity on just how the downscaling will work for old raids and the like.
Ion's words make perfect sense. For some reason some players seem to feel like the soloing of old raids isn't something Blizzard wishes to support, cares about, or even likes. But they've introduced ever more incentives to play the game this way -- as Ion notes -- with transmog, achieves, titles, and more recently with the addition of pet drops and changes to encounter design to make soloing more straightforward. That they would remove that gameplay with the squish is highly unlikely.
But some more news on just how the scaling will work is welcome. The percentage-based idea of damage makes it easy to understand how the squish will work, and how your experience soloing old content won't change. The numbers that cloud your screen and drop your framerate when dealing with trash will simply be a few digits shorter.