The whole "Iron" part sounds very ominous, not just for the Latins but the Greeks as well.
It reminded me of a passage from the coronation of Helena I Drakina. From post #8530 on page 427 in the old thread:
"Moderation, as Aristotle would have said, was the key. The Third Empire had relied too much on gold, and the Fourth Empire too much on iron. The Fifth Empire would be, hopefully, an Empire of Gold and Iron, combining their strengths and forgoing their weaknesses. The same as them, but at the same time also different."
Seems to me like the Empire might be loosing its balance once again. Maybe not surprisingly, given the name of the current ruling dynasty. And honestly, I don't think it's possible to end the Latin threat once and for all. No matter how devastating the war will be, a few generations later everyone will be ready to fight once again.
And what would the ultimate goal be anyway? Crush the HRE? All that would accomplish is an even more overpowered Triune Kingdom, who are already the more serious long-term foe for the Romans, and are basically untouchable no matter how much Demetrios might want to crush Latins. Sure, let the vultures circle over Germany, but I see little gain in actively helping the Triunes annex everything up to the Rhine.
Instead of satisfying some revenge fantasies and marching an army on Vienna or even Munich (which would face the same supply constraints as the current allied army), Demetrios should try to get peace as soon as possible. Let the Empire heal. Focus on keeping the Triunes out of Eastern waters. Dislodge them from India, maybe push the Portuguese and Spanish out as well, while you are at it. Helping the Mexican Komnenids destroy business in the Caribbean is also a great idea, that they are already pursuing. All those have much better immediate and long-term payoffs.