About to embark a migration of a WPF application that uses ViewPort3D. My 1st research shows this class is not supported on Phone 8.1. Am I correct? And if so, what are my options for migration?
To my knowledge there isn't anything similar to ViewPort3D in Windows Phone. That leaves you with a couple of options:
Use PlaneProjection to re-create the 3D effects
This is very limited in what it can do relative to Viewport3D, but if your application is only using simple 3D effects, then it may suffice.
This gives you the full set of graphics capabilities, but requires low-level graphics programming with C++.