The H1 bus speed is not appropriate for machinery control, but it is certainly good for closed loop control in process automation, where control cycle times of 0.25 to 1.0 seconds are commonly used. A very rough estimate says you could get 50 transactions per second. If you leave half of these for unscheduled messages, you could have 4 samples per second for up to 6 control loops, or 1 sample per second for up to 20 loops (which is probably more than you would want to put on a single bus segment).
The exact figure of 31.25kbps was chosen as a binary fraction of a 1MHz crystal oscillator (divide by 32).