The most significant changes to NIST SP 800-53, Revision 5 include:
In addition to the control updates, additional supplemental materials will be available immediately or in the near future, including:
And with SP 800-53 R5 out, several other items will follow along.
We'll be getting a revised 53A and the new 53B.
Other updates for FISMA documents should follow.
And as SP800-171 is based on 53, I would expect we'd see an update of that as well.