Addon Interfaces: background?

I am involved in designing a new system one component of which will
activate and manage a varying set of functions each with its own user
interface. The current plan, not yet well-defined, would package the
individual applications and GUI as DLLs and use dlopen() and its
associated functions to summon the required apps as needed.

While browsing 6.3 SP1 online Help, I discovered the Addon Interfaces
Library Reference. This looks like an abstraction of what we want to
do. Can anyone comment on the origins and usefulness of this