Actually, if you uncheck the "Name" and switch to say "AT" or "Power", then it will reduce the list to whichever you have selected. I just tested it and it's SUPER quick to respond as you type each letter. This doesn't help with level sorting or anything not Name/AT/Power related as it appears to simply be a keyword search function.
I also did another thing as a test. I tried to add another "column" of data to the playerslot file in hopes to see...Anything change in the server list (Added "Controller" to an alt), but what happened in the end is that it simply matched the server side list with my local side (for the sorting purposes) and wiped the erroneous data. So customizing that file outside of an external app to adjust sorting is out of the equation.
Now IF one were to make such an app for offline usage that could also read the live data (think HeroStats, etc), then you could auto-magically adjust the sort order Before you go into the game. I HIGHTLY doubt you could do this without a full restart of COX as it syncs the files (but IDK when in the login process), so the utility of it wouldn't be that high for on-the-fly sorting.