If the newest models also have a user replaceable SSD is still unclear.

Before you get to excited about the possibility of upgrading the Macbook Pro however, you should keep in mind: The SSD is still in some proprietary format, which makes upgrading rather difficult and expensive. In a teardown, which was done by the component-upgrading service OWC, something surprising was revealed: The SSD in the smallest Macbook Pro 13 (without the Touchbar) is not soldered down, its still user replaceable. In the specifications of the new models, the SSD was marked as 'Onboard', just like the soldered RAM. With the newest Macbook Pros, Apple seemed intend to kill even that last bit of upgradeability and follow the trend of the Macbook. However, one thing the user could still change was the (now proprietary) SSD. One year later, when Apple launched the Retina models, things started to change fast: The RAM was soldered down now, the battery was glued down and ODDs were completely gone, of course.

5 years ago, the then current Macbook Pro Notebooks had a fairly maintainable design, the RAM, the 2.5' SSD/HDD and the ODD could be replaced and upgraded effortlessly, although they already were less open to the user then the non-Unibody Macbooks. Apple systems are moving towards integrated, non-upgradeable designs for years now.

2017 mac mini teardown