I don't imagine the overhead will be too bad though, so it may decrease latency while keeping throughput essentially the same.
Of course you'll want to benchmark on your specific load. For example, at my day job it'd make no difference because we don't use threads, each Passenger worker has just one thread and handles one request at a time.
Python’s “new gil” (it’s some 15 years old...) uses a similar scheme, with a much lower timeout (5ms? 10?), but it still suffers from this sort of contentions, and things get worse as the number of CPU threads increase because they can hand the gil off to one another bypassing the io thread.