You are allowed to start a feature branch off of any branch, not just develop. IMO you should also be able to finish it into that same branch. You may want an experimental branch but keep the same workflow.
I have a pretty large feature request that's broken into many sub features. The ability to start a new sub feature and merge it back into the feature branch from which it spawned would be hugely beneficial.
+1 this issue.
I've been using my branch exactly for that for a couple months now
This is sort of implemented in my fork git-flow AVH Edition. More info about the implementation can be found at git-flow AVH Edition Issue 43
Any updates made to git-flow (AVH Edition) are almost impossible to make into easy pull requests for the original git-flow. The source code of the fork has diverged to much to make this an easy process and therefor we won't.
#278 it's there as well
+1 For this issue too! Any change to have it one day ? thanks.