There should still exist one well-known unencrypted page. Sometimes, I need to log in to hotel or airport wifi and therefore need to accept a MitM attack. I would prefer this not to be the case.
Hotel or airport wifi operates in that way because they can do so without inconvenience too many customers. If it becomes too cumbersome that they need to send in a technician every time a customer is not a sysadministrator who can figure out how to get the wifi to work, then market forces will make sure that they use something else.
The solution for all wifi clients is to do what iOS and Mac OS X has been doing for years, which is validate internet connectivity when connecting via wifi. If there's a captive portal standing in the way, it pops up a simple webkit view automatically. You don't even have to open a web browser.
It would be nice to have a more formal standard (e.g. supplying an authentication URL along with the DHCP response) but to be honest, this emerging de-facto standard is perfectly serviceable.
On the rare instances where it has failed me, I have diagnosed the problem to be the router allowing (or faking, not sure) a success response from http://captive.apple.com/hotspot-detect.html
If anyone has coded a captive portal to behave differently when it sees captive.apple.com they should be ashamed. All they're doing is making life difficult for everyone unnecessarily.
Google should do it on 8.8.8.8 just to make it more famous, but in general think about the meta websites defined in the W3C/IETF standards, such as: http://example.com
