The problem is not really in the toolkits, it's in looking at how the performance emerges from the design. Layout is the fundamental reason why GUI updates can be expensive: if you reduce it to a more static form, layout becomes cheaper, so recomputing it frequently becomes viable, and you can start caching more results without causing trouble. What's the reason not to use static layout? Configuration. But configurat…
I guess you don't make music, which is what this post is about. If people didn't want configuration, they would use Audacity and just record. How are you going to paginate a synths oscillator? Volume meters?