Why can't you automatically merge all the branches for testing? Sure, sometimes it won't cleanly merge, but then again, features behind toggles won't always work well together.
I once wished this were possible too, but in reality it isn't.
With n branches there are n! permutations to test. That's a lot of infrastructure to maintain and computing power to spend and you still don't end up with a single team-blessed deployment artifact that can automatically be promoted for manual testing or release.
Don't get me wrong, feature-toggles are indeed a pain in the ass, but in my experience cherry-picking branches to merge really is much much worse.
And with n feature flags, aren't there also n! permutations to test, that is, each combination of enabled/disabled? If you say no, because you just test features as they get manually enabled, why can't you do the same by manually selecting branches to be merged?
Yes, that complexity does not go away. But you only need one delivery pipeline, with one test/staging environment. Toggling and running acceptance tests against the variations can be automated, but is viable when done manually.
