I'd like to see Extra at 25% of all licensees, but something tells me that'll never happen.
Why would you like to see it at 25%? It shouldn't be. The extra class should be reserved for the best and brightest hams. It would be around 10% of all licenses. It shouldn't be a license you can get after a weekend of memorization.
I agree that the Extra shouldn't be a license that can be earned after a weekend of memorization. In fact I think no amateur license should be that easy to get.
But I don't think there should be a certain percentage goal, or limit. I think it should be something all hams could at least shoot for.
Fun historical observation:
The modern Amateur Extra was created by FCC in mid-1951, but from February 1953 to November 1968 it conveyed the same privileges as the General, Conditional, and Advanced. With its 20 wpm code tests, additional theory and 2 year experience requirement, few hams bothered to get one. By 1968 there were only a few thousand Extras out of over 250,000 US hams.
I remember well how, in those late 1960s, hams much older and more experienced than I said that the Extra was the realm of engineers and professionals, that only a top op and super-genius could earn one.
But then a funny thing happened.
Once the new rules went into effect, hams of all ages and backgrounds simply got one. It turned out the license wasn't nearly so impossible at all. The number of Extras grew and grew all through the 1970s, even before the tests changed, Bash books, etc.
I, being a teenager too stupid to know how hard it was, simply got one in 1970.
IMHO pretty much any ham can, if they want to.
73 de Jim, N2EY