The society you refer to techneut and which I opened was shut down because of lack of interest from anyone.
I am not sure how the NSCS is doing business(even though I am a lifetime member

), however the idea of chapters is about right
The idea would be basically for the Society to have reps in each city/university/conservatory. Then each one would promote the society to its own community and hopefully begin to organize concerts under the auspices of the society.Let me try to explain my idea with an example and I will use myself,since I know my area and such:
-The society or myself create posters,handouts and such. Then I would announce the "chapter" (to use techneut's suggestion) as the Texas Piano Society Chapter or something like that(the name is just an example)
-I post those posters/handouts at my university and send to faculties of other universities within my area(in my area,we have about 2-3 other universities).
-As membership would be free,I would expect to have many members join in. The only requirement for membership would be to be active on the Piano Society website with recordings and/or forum postings
-Then as the chapter grows, concerts under the auspices of the Piano Society and the Texas Chapter can happen.
-If needed, a specific rep per university within the chapter could be named and that rep would report to myself(chapter rep) every 2-3 month with a list of new members and such
Also,if we combine that with the book that is being done, the society could have its chapters membership free, while selling the upcoming book for about $20
Not sure if what I just wrote make any sense,but again it is just an idea that may need some tweaking to work.In any case, the above is my thinking