I’m leaning towards making Coronastien a seperate engine.
Aside from the inefficiency of loading the same map twice, achieving what you describe would be easiest with two seperate engine files anyway. Isometric maps use isometric tile images, which would look truly bizarre as Coronastein walls. Instead you would have an isometric map and an orthographic map for the isometric view and the 3D view respectively, loaded into MTE and Coronastein respectively. Then you would simply fade one to reveal the other and vice versa.
Of course, this does not account for the new possibilities afforded by Graphics 2.0 for Corona Pro users. I joined the early access program at the worse possible time- between releases- so I have yet to look at it. I’ve been occupied working on isometric map support for MTE lately, but I hope to get some more work done on Coronastein this weekend and sometime next week.