The use of stable in our infrastructure and understandably conservative rules for backports, stable updates and infra changes make it very difficult to even test something like Build Profiles (or Mulitarch builds) (which need changes in build tools and core infra), never mind get them into widespread use, without waiting for a whole stable release cycle (these are just recent examples - it's a general problem).
So this also means that it takes 2-4 years to make a change, which hampers progress. This session is a discussion on whether we can do anything to be a bit more nimble than this?