The current maximum of 9999 can be very limiting when having a custom numbering system (I use a 2-digit prefix that identifies all rules for a single destination IP and a 2-digit suffix for the rule number for that IP). I'm running into a situation where I need to configure more than 100 sub-rules for a single destination IP, this means I'd need to break my numbering system.
An easy fix would be to increase the maximum to 99999 or even 999999.