I wouldn't be surprised if this ended up a specific project, like Apple say we're not buying any more Intel chips with intel igpu. THey've used AMD only for add in cards for a while, their professional cards use AMD, that means most of their work accelerating software for gpu is done with AMD in mind currently. So maybe they basically demanded Intel use AMD GPUs for a specific line of chips solely for Apple, in which AMD/Apple can work together on the drivers.
There are rumours of Apple pushing towards their own ARM chips for desktop/professional products but that is probably some time away so this could be a stop gap measure, next few years of Intel CPU + AMD GPU. Could also be a stopgap till a year or two from now where they go AMD APU in laptops and AMD CPU + discrete gpu in some desktop and professional.
Either way, it's a win for AMD because even if AMD does amazingly well with Zen, Intel will still have the majority of the marketshare, so if you can profit from a bunch of Intel sales as well it's win win for AMD.
If you think about it solely as giving Intel uses the option for an AMD gpu means someone won't buy an Zen APU, then it would be bad, but if you think about it like AMD can win say 15-20% of the marketshare then also maybe have AMD gpus on Intel chips in 10% of the rest, that is still a huge amount of extra chips being shipped... it also means support for AMD in a whole lot more systems.
Will be interesting to see where these cpu + on package GPUs might end up, also assuming the rumour is true. Though one of the sources is generally pretty accurate and the other is, a bit of a **** but wouldn't often stake his reputation on such a big incorrect claim.