I would be very reluctant to use SQLite in such a situation, out of fear that “this is not really the sort of thing that its designers (probably) had in mind.” I am categorically nervous about going too far outside the envelope.

I'd love to see the basis of your fear. Is it founded in some documentation you've read? Or some demonstrably practical limitation you've encountered?

My question above was based upon practical experience of SQLite 2 where writer starvation was a frequent limitation in high concurrency use. salva's demonstration of 800/s throughput conclusively scotches that as a problem with SQLite 3. And further research leads to specific documentation of both the original problem and the solutions implemented in SQLite 3 to address it.

In the absence of relevant hands-on experience, gut feel is a notoriously bad indicator of anything.