I think it was about 15 years ago now that the ham radio license classes where consolidated down to three, from more than 5 different classes.
In that time I have been hoping someone would propose a new license class. I think there actually was a proposal that went no where to create a communicator license class. And about the same time the HSMM working group also proposed a licensing scheme.
More recently, while not a specific license class, Bruce Perens pushed for a major rules rewrite. His proposal had some good ideas to promote experimentation.
In order to keep ham radio relevant and interesting really relies on innovation from technically oriented hams. From there it usually progresses to small manufactures to adopt the ideas and put the stuff in the hands of many.
It wasn't that long ago that I myself was looking for a way to have a few of the outdated data rules relaxed so that I could experiment with 70 cm HSMM. And we are still in limbo on that many years later.
The quickest way to have rules relaxed so one can commence testing something new is to apply for Special Temporary Authorization (STA). A number of hams have gone this route over the years, and use that as a basis for a formal rule chance that benefits all hams.
The problem is that is a somewhat cumbersome bureaucratic process. The other problem is there are a lot of arm chair lawyers in the hobby. So if you don't go that route and decided to commence testing on your own, you risk really upsetting the community, even if whatever you are doing is only a little grey, and doesn't really impact others.
So I think we need an easier way to let the few folks that do the most good for the hobby (developers), get on with their ideas.
So I think introducing an experimenter license class is something to think about.
You ask, what would a new license class possibly offer anyone, as a general class license already lets you operate on all bands?
I am thinking those who took passed the experimenter license exam elements, are void of having to follow some of the rules.
Perhaps if they hold the experimenter license, their spread spectrum transmissions are not second class to all other modes, for example. Perhaps they are allowed to run wider data modes, etc.
I am sure its a contentious idea, but I do think, only a handful of folks would ever even pursue the license class, so it's impact would be minimal on normal operations. But I feel it would provide an avenue for more experimentation.