We are in the home stretch here! No new bugs have been discovered, the module seems to be working well, and testing is really helping. But there is one major-ish new feature that has been added (and I know this might have made more sense as a beta than an RC but my fingers typed rc before beta and here we are! Sorry about that folks) which I would love more testing on.
If you look at the page source, the fonts from the various providers get added via inline link tags. Going down the path of using drupal 8 libraries seems, frankly, unnecessary when loading fonts. But the same was being done for the font display css (which was actually inlining the whole css). The change is: the font display css is now stored in files (yay!) and exposed on a per-theme basis through using D8 libraries (double yay!). Testing is confirming that this is working nicely. However, I want to make sure this is working in the real world and that the upgrade for this is also working nicely.
TLDR: No new bugs, added new feature, need help testing new feature.