By the way, the roadmap link on the Github repo page is broken (though I did find it in the project's website).
I saw you're interested in handling Bezier splines. This might be premature generalization, but would you want to support whole BREPs? Is that something that is used in applications? I imagine lenses are generally simple geometries, so perhaps not.
Honestly, the main challenge at this point feels like finding the time / resources to just work on everything I've got on the roadmap. I think I've got enough ideas for at least 1y of full time work, perhaps more.
Bezier splines are interesting. I actually had a working implementation a few weeks ago, so I know it will work. It's just that I refactored the internals of how surfaces work and didn't port the old bezier spline code yet, but it shoudln't be too difficult.
I haven't given too much thought about volume representation so far. Currently it's just a list of unconnected surfaces which seems sufficient for now.