Yeah the procedural mesh component has some serious concerns as far as performance goes if you are creating a lot or very large mesh sections. There are a ton of optimizations and ways to improve it but it requires a modified mesh component to really pull off correctly.
You might want to also base your polyvox code off of their cubiquity branch for UE4, it has been recently open sourced and has a lot of additional features over the base library, I would use parts of it myself except I barely have any of the original polyvox library left in my personal project.
ANL is also a little slow, noisePP is a threaded and more optimized noise library that you might want to check out to improve more complicated noise generation.
Nice write up though and cool project!