I think it's a mis-phrased question.
You would have to look at what causes the high pH. I tend to think pH itself is a fairly unimportant measure. It's usually an indicator of hardness, and hardness is the real (but harder to measure) indicator of how fish will do, Nature doesn't read textbooks so pH and hardness don't always go hand in hand.
I have a good friend who is on a well. The aquifer he draws from gives the freaky water we're discussing - softwater up around 8. The local fish are the standard local assemblage - bass, perch, dace, etc. He has about 15 species in the small streams around his house. But they aren't unique to that water - they also occur in nearby water from other sources. If you travel a few km to the northwest of him, the water is hard from the wells. But the wild fish all around are the same unspecialised species.
He's a fish importer with a good sized business drawing from his well. I've seen wild caught Discus, Apistogramma (he only deals with wilds), wild Betta species, etc with fry in his tanks - with untreated tapwater.
One anecdote, but for years we noticed fish would easily breed in his pH 8, and would not in my then pH 7.4 tap. I had three times the hardness he had.
I used to breed a lot of Apistogramma (I had to modify my tap with RO). I was able to take wilds caught in pH5.5 and breed them in good numbers at 6.8, if the mineral content sat at 30-40ppm max.
To me, the question is off target. If pH is largely unimportant, and hardness, which we rarely mention is key, then why worry? The interesting question is hardness. There are different minerals in water in different places, and what effect do these have? I doubt we aquarists will ever be able to measure that with our resources, but it matters. Whatever causes a high pH in soft water is interesting. Which mineral affect which species and how? It's mind boggling. But the question people aren't answering is over simplified. I can tell you pearl dace, sticklebacks, sunfish, rock bass, yellow perch, smallmouth bass, banded killies, johnny darters and a catfish species all thrive in the small river/stream behind his house, fed by that aquifer, but they thrive over northeastern North America as well.