I like the beatsync feature, but I’m not a fan of the built-in timestretching algorithms. I prefer Akai-style timestretching as found in e.g. the open-source Soundtouch library, used by Audacity’s “Change tempo”/“Change pitch” effects. If more algorithms (Soundtouch, maybe Rubberband, both FOSS) could be added, that would be cool, but…
Perhaps a better option is to allow scripts and tools to provide new timestretching methods. It could be a callback function that receives the amount to stretch as a percentage or multiplication factor or just the target number of lines and returns new audio.