We cannot address every area of the application in any given development cycle. We certainly have experienced guitar players in the development and testing teams. Both of the developers who would typically work on guitar notation were fully occupied with the improvements to chord symbols for the entirety of the Dorico 6 development cycle. (And they are in fact still working on some of these details for 6.x maintenance releases.)
We will certainly come back around to working on guitar notation, of course, but here we are only 24 hours after the release of a major version, and it’s simply not possible for me to say when that will be. I hope that you will find many other improvements that are useful in the software despite the fact that we have not been able to improve chord diagrams in this release.