With the addition of new endgame content post HOs, tanks have definitely become less important than they used to be. Several things however will never change.
Agro management will always be needed on the majority of team based activities, perhaps not mob to mob but overall mob control is important.
A well built Brute may be able to do 90% of what a Tank can do, but a well built tank will take a pounding better than a well built brute.
Different armor sets will always have different strengths, that WP brute might out live that Fire Tank, but compared side by side with respective builts tanks will always be top dog of survivability.
Big fan of IOs, but the advantage for IOs won't go to the highest performer, but to the middle of the pack group (brutes) it will help them close the distance to having tank worthy #s.