Adjustments to OFF already happened on the 1.2 playtest which you can see here:
Most bosses minus this list that I made a few weeks ago can be frozen for some time.
Also to make sure ur OFF / BT work properly for endgame there are dedicated sets for them in The Mageslayer - Item sets - Grim Dawn Item Database and Rimetongue - Item sets - Grim Dawn Item Database .
About celestial/superbosses being trap/freezable… not sure if that would be a good idea cuz it might make them too easy. Would be great however if the dmg portion would still work.