Make PB having a pluggable architecture, where additional static Thought types could be added. Those Thought types would be fixed at the Thought creation and can not be changed.

Those static Thought types would have their own user interface tabs, depending on the type. The Thought type would be like a sub-application to the brain, with its own preference setting and options.
Third party programmers can create they own Thought type and plug it in to PB.

Anybody could add they own Thought type based on the PB pluggable integration specification.