Cellebrite has been operating with their present capabilities for several years. I can see few reasons why Signal would choose to publish a blog post such as this now, if not for the fact that a couple months ago Cellebrite write a blog post that specifically mentioned their ability to extract data from Signal (which, to be clear, was not a specific vulnerability in Signal). This prompted a very pointed response from Signal, which you can read here:
https://signal.org/blog/cellebrite-and-clickbait/. The timing makes it pretty obvious that Signal/Moxie took this personally (to say nothing of the general atmosphere when that blog post was written) and then took a few months acquiring a UFED and exploiting it, the results of which we're seeing now.