Oleander is correct. They did say in a comment that the Tribunal will not be returning in the form that it was in previously. The old system did allow for players to review all sides of a situation, but it had many flaws; the two biggest arguably being that it was incredibly biased and that it was extremely backlogged. It would take a while to find it, but if you looked through the Red Tracker posts about the Tribunal, you could probably find where they discuss about how players would sometimes vote all punish, or all pardons, for no apparent reason. And by running quality control tests, they were able to detect many false positives, where innocent players were being punished - which they could then fix.
The other problem, and the one that was probably the driving force behind the creation of the Instant Feedback System, was that the Tribunal was extremely slow. It was backlogged by thousands of cases, and it would take months for players to receive punishment for matches. Often, the players did not even recall the matches that they were being punished for, and consequently, the chance of actually being able to influence a player to reform their behavior was very low. By using the automated system, which is much faster, players are able to receive logs within minutes of the most recent game that contributes to their punishment. The game is still fresh in their mind, and if they are serious about wanting to reform their behavior, they can at least remember which behaviors they should focus on changing.
Riot has mentioned setting up some sort of alternate form of the Tribunal in the past, but I've not seen details of it ever posted, and I do not know if they ever made any concrete plans to that effect. The Arbiters also ran a small experiment on the Player Behavior sub-board, where they posted full game chat logs from volunteers, and players reviewed the logs in the manner that the old Tribunal functioned. They may do something like that again in the future, but it was something that was just done here on the boards, and not official Riot punishment review.
