I am almost sure that there will be problems. There will be patches of code that might require a bit of a rework. Not just change lib/functions but more fundamental ones.
And I do expect a performance hit. There are just 3 cores available on Quest. Probably I will try first modifying multithreading on PC to check how does it work with 3 cores. And I might have stick to smaller levels only. For graphics, I will probably disable some stuff and simplify meshes by having less subdivisions. Then, I will be also adding foveated rendering, which will also help. I am more concerned about CPU but there's nothing that can't be solved :)
I wonder if it is possible to feed camera into background. I actually like walking with Quest on seeing what cameras see ;)