To what end Can the Rhomans put this war on to an offensive footing? There is Croatia and Aquileia that could be brought to terms, which could lead to a bigger hinterland for Venezia. They can ravage Hungary, which would only make the axe the court of St. Stephen is grinding, double headed. They could put Vienna under siege, the Danube is theirs so long as both banks are secure. They could draw on the naval capacity of both Egypt and Sicily to really shake up the W.Med, and the approaches around Iberia and W.Africa, this however would sour relations with the Iberian states.
If these ideas have flaws please say so, as I am spit-balling because it seems a lot of the discussion is leaning towards just the campaign in the Haematic peninsula. This is going to be truly WW0, and I feel that Demetrios has a streak of Machiavelli in him and understands that if he wants to have even a decade of "peace" in his reign [if it lasts that long (which I hope it does, he is my favourite character in this story, and has a chance of living up to his namesakes appellation of Megas, just in an economic and political manner)], he needs to break his enemies so that the thought of a war with Rome is the last thing on their mind. He also needs to finally secure from threats, if not stabilize, Rhomania-in-the-east.
This war is going to set the stage for the geopolitical world for the century to come. I could even see if the Rhomans win, mesopotamia will be next to be quieted. The Triunes are building a threat to Romes eastern trade, through the Ottomans. Yes that would be a generational plan of build up and attack, but again I feel Demetrios sees the long game better than most. Also the thought of a descendant of Timur sending Rhoman armies to bring the Ottomans asunder makes me smile.