I'd guess the next LR will be released sometime between tonight and the end of the year. There are more cameras than the D750 to support and LR typically comes out every 3-4 months with the last update being July 31st, so you do the math, although Canon has announced a new 7D Mark II camera that will be for sale the end of November so Adobe might wait until they have that camera in house to add it to the next version of LR, as well, before releasing it. If Canon loans Adobe a camera before it is available for sale then LR could have support any time, but if Adobe has to wait and buy the camera it might not be until a couple weeks after they get it at the earliest. Adobe might also not care about the 7D Mark II in this release, and it could be sooner, but then the Canon early-adopters would have to wait 3 months and a different set of people would be asking the same sorts of questions.
Rather than posting in the Adobe Camera Raw forum which is generally about the Photoshop plugin, I'd suggest you search the actual Lightroom forum for D750 and you'll see answer to how you can use your new camera with LR, now, before the next release, assuming your OS and hardware are new enough to meet the LR5 system requirements.
C'mon Adobe, what is the wait about? teaching those "pesky Mac users" a lesson? I am not being able to use YOUR product on y Mac Pro because you just can't give all platforms the same weight...
Raw updates usually come out to cover a group of several new cameras at once, so they normally don't come out immediately after just one camera is released. They do come out at regular intervals and we already know that the D750 is supported in the pre-release version of Camera Raw 8.7 on labs.adobe.com, so they're probably working on it for Lightroom too.
It isn't clear why you think this is because Adobe is somehow anti-Mac, because the Mac and Windows versions of Lightroom are always updated at the same time. The current version of Lightroom for Windows doesn't support the D750 yet either, so Mac users are not left behind.
When is support for the D750 coming to Lightroom CC Mac?? You'll loose me as a customer if not VERY SOON!
Apple also has camera raw updates that they release for OS X, so if you want you can leave Adobe and stick with Apple software. But if you do, keep a couple things in mind: Apple has not released a digital camera update for the Nikon D750 either. And, when you look at the past few years of raw releases from Apple and Adobe, Mac users often get support for new cameras from Adobe first.
A lot of Mac users seem to think Adobe is against them. But as a Mac Pro owner myself, I've seen that Mac users often get support for a new camera from Adobe sooner than from Apple. And right now, because the wave of mobile apps that Adobe just released are only for Apple iOS, many Android users are under the impression that Adobe is completely pro-Apple. (I don't think that's true either.) So if you think Adobe is not giving platforms equal weight, consider that the weight may actually be in favor of Mac users.