I've written a PowerShell script to allow you to get a free SSL certificate from Let's Encrypt to use with FileMaker Server. You can schedule this to run every few months and renew your certificate automatically. Now there's no reason to keep using that default certificate. Check out the post for instructions!
EDIT: One incompatibility which has been discovered is with FileMaker Go 14. While FileMaker Go 15 is able to validate everything and connect, it seems that Go 14 doesn't see any files available. There don't seem to be any problems with FileMaker Pro 13-15.