The apparently irresolvable problem is how to leave a 16th Century dispute in the 16th Century. The Decet Romanum Pontificem declared that Lutherans forfeit their right to own property. Although this declaration has not been rescinded, the events giving rise to it have receded into the shroud of antiquity. Similarly, the Lutheran statements on the Papacy should be read in the context of the time when they were made.
There is no easy way to handle historical disputes. What is ironic is when, let's take the case of the 30-year wars. Many of the freepers who argue on side A or side B may have forgotten that their ancestors may have been on the other side, or indeed in the intermingling, perhaps they had ancestors on BOTH sides
And of course, we forget sides c, d, e :)
With regards to the Decet itself, the first minor, very minor, step we Catholics have made is saying the Church will reconsider. The second, big step that we must make is rescinding the added piece of "those who follow him" -- it's too ambiguous and unlike that against a specific individual is not time-constrained.
The third step will require a lot more prayer and effort on both sides and we should not focus on this right now so much as the above two