I heard a rumor, that they use standard connectors in the future. The signs are:
• NVMe support in newer OS X versions.
• TRIM command support in newer OS X versions.
..which make no sense for FUTURE OS X versions, if Apple does not develop computers which use standard connectors (i.e. user replaceable SSDs).
The connectors are standard. Unless you are taking about the new laptops where everything is soldered on, and that ssds look like ram chips.