I read this post when you made it and see that you linked to it in a different post. I'm not going to say this is wrong but I do think it is a little far fetched.  Most likely ISPs will abandon their email platforms as the majority of users already have an account such as gMail or Yahoo that is not tied to an ISP.  This allows users to switch ISPs or move across the country and not have to change their email address.  What I do not see happening is the business world shutting down their in-house email platforms and migrating to the previously mentioned providers.  The business worlds wants control, security, and privacy and the only way they can do that is by hosting their own.  It may be a Microsoft/Outlook based system but they still managed it themselves.