I worked on CRM and Marketing automation software for quite a long time, and we always maintained lists by doing staged cleanings. We would place people in segments based on their interaction until we hit that point where we would move them to an inactive segment completely (but they may have gone through 10 segments first). We would occasionally target the inactive list with special offers but in general we didn't do it with regularity. The lifecycle and journey of the email through different segments was really quite specific to the client type and the journey type.

So to answer your question more directly, it is a critical part of what people need to do to have proper response rates and to minimize issues with third party filtering systems. There is an absolute need for this type of stuff, I am just not sure if there is a large market opportunity here. Enterprises should be doing this already so you target would probably be SMB's and other similar businesses, which means lots of work for low dollar sales most likely. Maybe I am wrong there, but that's my initial thought.