I'll chime in here just from my usability perspective. The tag system is quite complex and requires several steps to really use effectively. As the default view for Assistant threads is the 'All' folder and the default thread life is 'temporary', you have to do multiple steps if you want to retain and then access a 'pinned' thread in the future as it lives in another folder which you also have to navigate to after the fact.
As I see it, a context menu addition to 'pin' would allow you to save certain threads in perpetuity in just two clicks (one on the context menu, one to pin), removing it as temporary, assigning it as pinned and then placing it above the rest of the thread hierarchy in the pinned section to be easily accessed at any time.
