This seems to be a really old thread but let me add my 2 pennies.
IIRC If you’ve declared a bypass parameter in JUCE via getBypassParameter, then I don’t believe processBlockBypassed will ever be called (although that probably wasn’t implemented when Dave first wrote this post). If you haven’t then yes I’ve certainly seen DAW’s call this in the past.
However, Logic never will call this method as its bypass is not actually a bypass it just stops processing altogether. Reaper should have two different bypass mechanisms, one will stop processing altogether (like Logic) the other should indeed notify your bypass parameter or call processBlockBypassed, but it’s been years since I tested that. I’m less sure about BitWig, but that actually sounds quite smart as it means you get constant processing performance which can reduce glitches due to sudden changes in processing.
See my comment here for more information