CAS custom functions sets
I think it would be useful that GGB had the possibility of create CAS custom functions sets and then save that sets in an specific format (.ggs .ggf).
Thus, with a menu option like "load custom functions set" any user could use an specific set of functions.
So, fields like physics, chemistry, economy, etc could have the opportunity of using their specific functions, without overloading the core functions of GGB.
I used to do that with DERIVE