Galbeedi,
I like your optimism, but there are few problems with any possible selection of Demeke Mekonnen, one being he was and is an effective participant in the war against the TPLF and by extension Tigrians and secondly, he needs a base. Though he is Amhara, no Amhara would support him if Demeke gave concessions to TPLF while the TPLF is conquering and displacing Amharas. The Tigrians won't welcome his selection as long as Amharas are 'occupying' Humera and Welkait. Thirdly, you are overestimating the influence Americans have over different groups. While the Americans can push the elites, they have little influence over the armed factions. There is a worry emergence of a warlord class that is not answerable to anyone.
And finally, I don't think we appreciate fissures within society and the level of hatred that might not be overcome in the immediate future. It will take a deliberate and delicate process to heal the people so they could see each other as neighbors and fellow citizens again.
There are possible ways that spare Ethiopia the hardships of Somalis. The competing groups can agree on a compromise candidate whose sole job is to transition the country to whatever agreed system of governance. Such a person will be hard to come by. Or different groups can establish a council that is representative of the country and keeps everyone in check till they figure out a way forward.