I would suggest sticking to the old version of Webkit until it is absolutely necessary to upgrade. My intuition is that it will be more work to try to maintain it up-to-date every month or so, than doing it once or twice per year, even considering the scope of the changes on Webkit.
I guess we can stick to the old version until it's necessary to upgrade and redo the instrumentation if necessary.
Hopefully, in the meantime, we might find out that integrating our engine in a browser will be less work than maintaining the current profiler.
This is what I would like as well, I think that instrumenting through our own engine will probably be 10 times easier. However, we don't know how much time it will take until our system can run in a real browser and support all of ECMAScript 5. Let's hope it's less than a year...
- Maxime