Here are my prep notes for the 1228 Rhine Tribunal:
I decided not to have the Grand Tribunal be something for the players to participate in but rather an event that they would influence via what happens at the Rhine one.
But big ideas that can happen at the Grand Tribunal of 1228 is the formation of a Lotharingian Tribunal at the expense of the Rhine.
Tremere machinations against house Bonisagus (lonked to the above)
A big push towards the "4th estate" overarching plot.