Should think It would have more affect on the need for fast wide angle primes! Really any need for a 24mm 1.4 anymore?
Have you ever used a 24 f1,4 L II on a fullframe body?? The look of the picture you get at that wide angle and that shallow depth can't be done by anything else.
Nope, never have, but I would certainly love to see an example of a real world shot using the 24 1.4 wide open [out of 100 shots - how many @ 1.4?] compared to ones shot at f2 or even 2.8 - real difference? care to share? Anyway, I didn't really mean to suggest that nobody would want the faster wide angle lens, but they are pricey, big and the DOF advantages aren't as obvious [compared to telephotos]. I'm simply surmising that many [most?] folks will find less need for them as high ISO performance improves. If Canon made a nice 24mm f2 L - I'd be all over it!
I'll go out on a limb and predict that across the board - high ISO cameras will increasingly cannabalize [not eliminate] the sales of fast [zoom and prime] lenses for ALOT of shooters - how could it not? Size and price really do matter!
Doubtful. People who would accept high ISO performance as an "alternate" to a fast lens probably were not interested in having a large, fast lens in the first place. They are not really equivalent things because, high ISO has different and distinct effects upon the final image than a wide aperture.
Let me also add that the fastest lenses also tend to offer other features that prosumer and professional shooters care about almost exclusively. Things like weather sealing, build quality, focus speed, etc are things that are important for those who are really serious but, not so important for someone who might just want to take nice pictures.
Finally, the only time when high ISO performance and a wide aperture are interchange is during low light shooting, and only when you can tolerate a deep DOF and slower focusing speeds. That's quite particular and, generally speaking, is only encountered when shooting a static subject. There are plenty of more times with a fast lens cannot be supplanted by high ISO, in terms of composition and in terms of focusing speed and accuracy.
But, you are certainly correct that lens and camera size and weight are important. But, then again, I think the mirrorless interchangeable cameras with M43 and smaller sensors do a far better job of reducing lens size and weight than high ISO performance does. I don't see any serious future changes to sales patterns of fast, heavy lenses just because new sensors are better in lower light.