It's definitely a well-considered approach. I don't have to care about the framework that's been used or set up a custom proxy to capture and replay / simulate API actions, you're literally recording system-level calls and that would be extremely valuable for replaying those annoying edge-case race conditions that seem nigh-impossible to track down without significant effort at replicating exact steps and timings.

I mentioned in my other comment about Windows support, but even better if you could do something like browserstack, where I could just direct users to a URL where in the backend you guys are running the replay browser, but from their perspective they're just "using the website", that would be a killer feature. "Here, go to this URL and make the bug happen again, as soon as it happens click the little bug icon" - wouldn't have to convince an IT department to allow custom software on their COE, I could foot the bill and pass it on in my invoices so don't need to convince their accounting to approve licensing, etc, and you wouldn't need to compile OS-specific clients...

Anyway I digress, really cool stuff and thanks for expanding a bit on how it works, taking something so low-level as syscalls and wrapping it up in a user-friendly interface is no mean feat - good luck!