They might end up being proven wrong on this prediction.
Absolutely a possibility. I would say, though, that when trying to predict these sorts of things, it is always important to assume that all parties will play their hands in an optimal fashion.
I think if Intel plays its hand in a fashion that's even within the ballpark of optimal, a 15% decline in revenue share in one year isn't likely to happen.
EDIT: Let me add to this.
So think about this from a business POV.
Let's say that 40% of the PC market is desktop, 60% is notebook. Right off the bat, 60% of the market is inaccessible to these Summit Ridge Ryzen chips. The remaining part is where Ryzen can theoretically play.
Now you're down to 40% of PCs, or the entirety of the desktop market. But roughly 50% of desktop market is consumer, 50% is corporate, and corporate buyers tend not to be interested in CPUs from AMD, let alone iGPU-less ones. So I'd say the market is pretty much down now to half of the overall desktop market, or 20% of the overall PC market.
Within that half of the desktop market that goes to consumer, how much of that is
enthusiast gaming? Let's call it 25% (probably on the high side here).
So now you've got these Ryzen chips going after the enthusiast gaming part of the consumer desktop market. Of your overall PC TAM you're down to:
1*0.4*0.5*0.25 = 5% of the overall PC market. Let's say that revenue share of overall PC market is 2x the unit share because of generally higher ASPs. So, 10% of the total revenue in the PC market for these Ryzen chips.
How much of that market is AMD realistically going to get in a year? 7700K is still arguably the best gaming CPU out there today (and it's at $350), and Intel can cut prices on Broadwell-E, has Skylake-X coming out, and so on. On top of a good set of products (competitiveness can be modulated with price movements), Intel's brand is stronger, relationships with the key system vendors is stronger (and those system vendors buy lots of other chips for their other product lines, so much easier for volume discounts), sales force is more comprehensive, etc.
Let's say AMD gets a full 30% of that enthusiast market (again, optimistic, but this is basically AMD's share of the dGPU market).
That's 30% of 10% of the revenue share in the PC market, or 3% revenue share.
3% of Intel's Platform revenues (i.e. CPU+chipset) in 2016 ($30.7B) would be about $921 million.
And from there, recognize that AMD's share of the gaming/enthusiast CPU market is currently non-zero (a lot of FX chips still get sold, and I'm sure people still buy those Kaveris on FM2+ for this purpose too).
That's why the estimate another poster gave of $9B revenue share loss on Intel's part in one year doesn't really make a lot of sense to me, but of course we will see.