While I agree that the 14-24 may take some time to materialize, your first and second argument are contradictory. As per your own argument the 14-24 will be a compromise of sorts so the IQ of the primes will be better. Prime shooters will still go for the primes regardless of the existence of the 14-24.
I partly agree... I think the 24L II is safe... it is a faster f1.4 and is safe from internal price poaching.
But the two f2.8 lenses (16-35II and the 14L II), I am not so sure: 16-35L II at f/2.8 though not a direct competition, is a reliable revenue generator for Canon and I think they will try to keep it even if this hypothetical zooom is planned ; but there will be some residual predation there as at least some who are currently forced to choose 16-35 II even though they have the money, will opt for the overlapping wider UWA.
Now the 14L II currently costs about $2300 and bears the usual crosses that UWA's bear (still agreat lens) may not be so safe at f/2.8. The hypothetical 14-24L zoom, even if it has a smidge less IQ, will tempt some, it will tempt me.
If this were the case, the 24-70 II would cannibalize the sales of the 24, 35 and 50 Ls. Don't see that happening.
This, I don't agree with. All three primes you list are faster at f1.4 or f1.2... with stellar reputation for the first two lenses and a controversial cult following for the 50L. not even a close comparison to the 24-70II at f/2.8. If you want faster, you will choose the L primes.
Now will one do the same with the $2300 14L II f2.8 prime if the f/2.8 zoom existed... I don't really know.