My understand is that the truss was designed to accommodate 10
unpressurized science payloads. I believe that AMS-02 may still be
alive as a potential science payloads, but I can't find any information
on any current science payloads for the truss beyond AMS. So, two
questions:

a) Are there any plans for unpressurized payloads for the truss?

and

b) What are some of the payloads that either were previously approved,
or at least got to Phase A?

The literature seems very vague on actual projects, although there is a
lot of data on accommodations for such payloads.