Maybe the security expert could read the readmes in the repos first. From the iOS app repo:

The initial development release has reduced security, privacy, availability, and reliability standards relative to future releases. This could make the software slower, less reliable, or more vulnerable to attacks than mature software.

And further:

If you're planning to use this application in production, we recommend reviewing the following steps: […] The Pin storage configuration matches your security requirements, or provide your own by following this guide Pin Storage Configuration […]

So the text hints not at design flaws but at facts that are already stated in the readme. Plus, the major source for the article is Pavel Durov, who’s messenger is of course a standard in security and privacy.

So there seems to be no news but a lot of speculation by Durov instead.