I think I have a solution to the rolling and releasing

Post LTS.  You start a rolling release. This gets all the goodness in that you want.  6 months in you take a fortnight out. Week one stabilize, week two ISO testing.  The resulting ISO is then supported with security back ports for the next 6 months till the next ISO is stabilized and so on till you get to the 6 months for the next lts.  Here you go back to the more tried and tested release method so this release is solid, stable and ready for the next 5 years.

This I think gives users a regular cadence they are used to. Gives people like system 76 a regular OEM install it has security back ports from the continuing rolling release.  It gives app devs a set of libs for 6 months that won't change.  And means there is only a fortnight slow down for the devs.

Plus the community driven derivatives can continue to use their current 6 monthly cadence. Everyone is happy :-)