Speaking as an operator there is a wide range of ways we use captive portal like tools. I’m happy to try to organize a presentation if that is helpful. Our definition of “captive portal” may be a bit broader than folks on this list may think, so it may be interesting.
One person who may have interesting thoughts to contribute is Steve Bauer from MIT, copied here. He has a novel idea for the need to have a portal-like communication channel to end users that he’s called “net.info” as a working title. I wonder if that might have some applicability here.