Hi Chipp, it's an interesting idea and sounds like a good possibility for the future. Things running on their own thread greatly increases the difficulty of the coding though so it might involve quite a lot of work to make it function smoothly. Fillets in NURBS involves a lot more complex calculations than in polygons so the threaded approach might be a requirement to avoid lots of waiting before being able to do more stuff. Also I'm not sure if it makes sense to put effort into increasing fillet robustness first before attempting that.

- Michael