IIRC Benjamin Franklin tried to make use of diacritics in his (U.S.) newspaper, and it didn't fly.
English could use a spelling simplification, but it's not going to happen -- it's too late and there's too much inertia in the current way of doing things.
Also, FYI, the circumflex in ê in French isn't there to change how e is pronounced but to denote that after the e there used to be an s that has been dropped, and that's how it always is for the circumflex accent in French. Sure, être is not pronounced the same as it would be were it written as etre, but I think that's accidental and not really the essence of the circumflex accent in French.
English could use a spelling simplification, but it's not going to happen -- it's too late and there's too much inertia in the current way of doing things.
Also, FYI, the circumflex in ê in French isn't there to change how e is pronounced but to denote that after the e there used to be an s that has been dropped, and that's how it always is for the circumflex accent in French. Sure, être is not pronounced the same as it would be were it written as etre, but I think that's accidental and not really the essence of the circumflex accent in French.