Architecting a Solution with many Sites within a Site (Chapters) - How many sections can Craft Handle?
As chapter numbers grow, will this be too many sections for Craft to handle?


Probably not.  I suspect as your section list grows to the multi-thousand section range (if it will ever get that large), you'll start to run into MySQL/environmental limitations rather than any Craft ones.  But if  you do run into any UI/architectural limitations, we'd love to hear about them.

In the upcoming Craft 2.3 release, we spent a great deal of time addressing UI scaling issues around Structured Sections and Categories when they start to approach the multi-thousand range, but we've seem installations with several hundred thousands of Channel entries/assets/users running just fine.