I already had 6.0.0 installed and did an incremental upgrade from 10.13 to 10.15, and did not run into any serious issues other than having to grant some permissions.  

However, other older software already in /Applications may fail to run after the upgrade (which was the case after I did one upgrade).

If you must upgrade, I suggest using Disk Utility to make a disk image backup of your entire boot or Macintosh HD partition so you can try to revert back using its restore function if necessary.  I've only put the upgrade on one machine because it is new Apple hardware that cannot run 10.13 or 10.14.  My advice generally is to always stay one revision behind the latest version of Mac OS - which right now would be 10.14 Mojave.  I don’t have or know of any software that only runs on 10.15 but does not run on 10..14.  So all my other machines that can still run 10.14 have not been upgraded.

- R.