A lot of work was done on cancellation/timeout in 5.0 (#3166), but the following remains:

• Break the connection when sync cancellation fails #3187
• Direct binary writes aren't asynchronous #2444 (cancellation was done as part of Passing the cancellation token to the write buffer #3163 but timeout still needs to be done)
• Improve connector's cancellation request #3277
• Implement cancellation and timeout on write #4647
• Multiplexing (user cancellation, not timeout).
• Add timeouts for every different user action #3341
• Gracefully handle prepended query cancellation #4909

/cc @vonzshik - we can add links here to individual issues to track the global state of things