I've done a lot of reading about the internal reflection issue, as I'm considering buying a D750. There's a LOT of discussion about it on Fred Miranda forums, and DPReview, but the common consensus seems to be that most of the shots you'll ever shoot into strong sunlight (or other equivalent) probably won't show it. It appears you have to have the light source in exactly the right place for it to happen - and even then it may not.
There seem to be many threads suggesting that several other bodies suffer similar issues - to varying degrees - but not many, if any, direct comparisons under the same, so it's hard to tell whether it really is a more prevalent issue with the D750.
I personally doubt that Nikon will acknowledge this and fix it - I think it's perhaps a storm in a teacup - there is certainly a reflection you can create on stills and during video, under certain conditions, but it's not that dissimilar to what I've seen from people testing other bodies for the same thing.
Let's be honest - if those wedding photos, shot into the sun, hadn't been shared on the internet, who would have actually noticed this? (I think they were first put on FM forums). How many people on here have noticed the 'internal reflection' issue on real world, every day photos?
I'm still not sure whether to take the plunge and go for the D750, I'm waiting a few more days, but my current thinking is that this wouldn't put me off because I'm fairly certain I will never notice it unless I really look for it and try to 'provoke' it happening.
For the record - Gary's issue seems to be a separate thing, a light leak or something affecting the left side of his images. I'd be very surprised if his replacement body shows the same problem again.