They are very different, it's been seven years of heavy development since forking. For comparison that's longer than the time between apple forking kHTML to make webkit and the the first release of chrome.
The question was "How different are Blink and WebKit these days?" and "But perhaps that has changed?".
My answer was "they are different" and implicitly "yes", partially because of the heavy development work that has been done since the fork seven years ago.
If you look at the featuresets and when they introduce features I think it's reasonable to conclude they have diverged enough that they can't just pull patches from each other.
Also, there was a webkit mailing thread back when they introduced their cut-down version of service-worker that said that most of the code from blink was basically unusable for them because of the differences.
My impression is they share patches enough, that they can't really be counted as different browser engines.
But perhaps that has changed?