Composer is optimized for how php executes which is once per request. If you want to compute namespaces per request that's your choice.

If you wish to daemonize it have a file change listener run it when it observes file system changes in the appropriate directory. If that is too much work a quick hack would be:

    watch -n 10 composer dumpautoloaf --no-scripts &

Full disclosure: I did not verify this command would work well