I would like to hold on the last frame of a trigger group (now called a swap set) while the key trigger is pressed and then play in reverse when released. I can't see any way of doing that in the new Trigger panel. Any ideas would be appreciated!
If you mean the "hold on last frame" option for cycle, you should be able to set that in the properties panel section for the applied cycle layers behavior and add that group with cycle layers applied to a trigger in the triggers panel.
That is, the cycle will be one trigger (for the group to which cycle layers is applied) in the swap set and not the whole swap set.
This may be made more confusing since the default drag and drop behavior for a group is to create a swap set of its elements, but the right click menu for the group should include options to create a single trigger for the cycle or to add the cycle as a trigger in a swap set.