Going back to all aluminum, are there ceramic coatings that adequately deflect/absorb heat that can be used on leading edges and other high heat areas?
No, n ot really. Ceramics are too brittle and don't bond well enough in thin coatings to stay with the structure as the aluminum flexes. You're better off with titanium.
The problem with titaniun is not corrosion or CTE (although that one can be a problem), it is cost, density and, worst of all, formability.
Aluminum forms easily and then can be heat treated to get the strength you need. Titanium is too springy to form worth a d@mn. To get it to smoothly curved shapes requires either machining it from billet (= $$$$$$) or superplastic forming (= $$$$$). While it is stronger, for most aircraft structure, it is stiffness that counts, so you really can't reduce the thickness of the material to counteract the increased density, thus whatever you replace with Titanium instantly becomes 60% heavier, which is a bad problem for an aircraft that is supposed to go fast.
In thinking about a super fast Phantom, your real problem is that the aerodynamics really aren't there to go a whole lost faster than the Mach 2 that the design is rated for. The Phantom really is as aerodynamic as a brick and would need a huge aerodynamic clean up and reshaping to hit much faster than about Mach 2.7 even with higher thrust and lighter engines.
Paul