These are the only ones that exist (that I know of, because they (macsales) work on/with the Apple hardware specifically to make the SSDs work):
https://eshop.macsales.com/shop/ssd/owc/macbook-pro-retina-display/2013-2014-2015
They are a little slower than the Home Grown Apple built-in ones on the read time, Apple's get about 1500 MB/s, where as macsales is claiming 750. But if you are retiring a MacBook 2015 to say your game room or something, or for some dedicated project, in say 5 years it's nice to know you can design what you need, space wise.
The 2016's are recyclable and "Soda Can Macs" Expensive as hell tho if you want a dGPU. I just don't know how they could last more than 5 years with heavy use on the SSDs.
I honestly think in 5 years they will phase out Intel Macs and go completely ARM based. With ArmBooks.
Where you could buy like a really fast 16 core "MacBook Pro" that has an ARM processor with maybe even LTE (or whatever is next) and then it'll only cost $1200, but will be comparable to a $2000 MacBook Pro... it'll be ARM and there won't be any "Rosetta" or emulation, and if there is it'll be slow emulation... it'll be fun tho!
I almost wrote a post on appleinsider.com, how I would just like Apple to fold and pay out all the money to everyone, because people don't know the future of computers Apple has more of a grip on the computing world than most of the guys who keep BITCHIN... it's a joke.
We get what we get stop complaining.
Look at the Playstation 4 and Xbox One and now One S.
They make essentially 1 model, and that's that, you either like it or shut up... Apple does a pretty good job of giving people 5-10 different choices!
There is ONLY ONE caveat to my Theory.
Intel's Optane architecture, I think this is Intel's only chance to keep a lock on everyone using Intel. Optane is freaking sick!