My issue with hardcoding any kind of preset priority, is that it can still be different from one person to the next. I've done a LOT of theorycrafting on the optimum FCFS rotation, and this is just a tool I used to help real world testing of different priorities. Things like your tier bonus or libram can definitely impact your priority list. Even things as simple as having an add pop out on the boss. For this reason, I wanted to make this addon hold as few hands as possible. It's a tool that should be primarily used for target dummy practice, or a quick way back into your optimum rotation if you had to run from the boss or change targets for a moment.
I know it will be used for more than that, but I don't really want to go down that road with the development. I've been considering options for the DS/SS timer as well. I've discussed that a little in the WoW Interface comments section and one of the users there recommended this addon for SS timing:
WatchSacredShield:
WatchSacredShield - Addons - Curse
I don't raid on a ret paladin and just theorycraft for a friend, so I'm not aware of the finer points of using SS or DS on raid bosses... if someone could give me a quick overview, and how the addon could help you with it, then I can look it over and see if it's something I'd like to put in.
Also, as far as only being enabled on bosses... I can look into it as an option. I'm not immediately aware of an easy way to tell the difference between bosses and trash though.