I have always wondered why the decided to put it in the D750.
Pure hypothesis on my part but I suspect Nikon wanted the D750 to be a serious contender for people who intend to shoot video extensively. I don't shoot video myself, so I may be speaking out of turn when I say this, but I'm under the impression that moiré patterns are more likely to be a problem when shooting video (??).
I know you removed yours early on. How has it been in the long run now?
I did have it done pretty quickly so it's hard for me to do any kind of long-term pre/post-removal assessment since I've done the vast majority of my shooting without the filter. I'll go out on a limb and say it might "up the ante" a little on getting the most out of the body, meaning it forces you to have really good shooting technique. For instance, you know how putting pro-level glass on a body that has been used previously with consumer-grade glass can sometimes require you to improve your shooting technique? Yeah... Sort of the same thing with having the OLPF removed. There is a definite improvement in sharpness but you also have to do your part. Hope that analogy makes sense...
For anyone reading this thread and asking themselves if having the OLPF removed from their D750 (or any other camera body) is something I suggest they do, I would say it's definitely NOT for everyone. It's not cheap and I'm confident it will void your Nikon warranty (if that's a consideration). That being said, yes, I'm glad I had it done; but that's me and doing so suits my type of shooting. I also don't shoot video... at all. Anyone who does should probably proceed with double-caution. So, yeah... In short, I would advise anyone considering having the OLPF removed from their camera to first consider how they use it and urge them to do their own research before proceeding.