I also used 'perf timechart'[0] in the past, or rather I tried to, but the traces on any realistic workload generated SVG files so large that it was too slow to open in firefox/inkscape etc. Your approach seems to be more scalable as it doesn't generate one huge image/SVG but rather generates that zoomable view via Javascript on-the-fly, right?
[0] http://web.archive.org/web/20130729151516/http://blog.fenrus...
- Show labels at a readable size, whatever the zoom.
- Keep labels within the screen bounds where possible rather than letting them scroll off.
- Fade out large-scale features (e.g. arrows spanning long time frames) when you get close, so they don't blot out everything in between.
- Project y values through tanh so you can see everything at once, but focus on the bit you're interested in.
Of course, there are other opportunities for adding interaction too.