The lighting differences between adjacent views in a panorama almost always result from differences in GI calculations. You can improve this by increasing GI Blur Radius and increasing GI Sample Quality. You might try GI values of 2 for relative detail and 4 or 5 for Sample Quality, with a blur radius of 50-100.
Spherical rendering is definitely something we want to add in the future. I don't have a time frame on doing so however.
- Oshyan