I wonder if we'd be better off using a different term than 'experimental'. I don't know if there's a 1:1 relationship between server stability levels and the potential categories of feature packs. Using a feature stability level name as a term implies there is.
A clear dividing line I see is whether the developers behind a feature pack are carefully following the WF Community Feature Process or not. If they are, then the feature pack can include elements at all sorts of stabilities, as 'wildfly-ee' itself does.
I've used the term 'incubating' before, but that's not quite right either. There can be feature packs that are not at all incubating from the POV of their authors, but their development is not following or cannot be confirmed to be following our processes.