Although that's a very nice idea it would be really difficult to extract safe results.A lot users don't know what services/apps running on background.What about widgets?What about settings on various apps?It's not the same checking weather every half hour and every 12 hours.Also some areas are poor on 3G signal so results will vary a lot.I propose for better results the following:
1. Roms installed just the way devs give them, no other modifications/installations except the program which measures battery drain.
2. 2G network settings with data transfer off.
3. Battery drain measurements over night at least 6 hours, 8 would be best and user should calculate his results e.g. 4% in 8 hours so 0.5% per hour.Calculating wont be that easy though, usually you'll have something like 4% in 7 hours and 23 minutes.
4. Battery should not be fully charged at the start of measurement, usually the ones that have a lot charging cycles drop quite fast from 100% to 95% .Under 90% is fine i think.
So conditions must be very specific otherwise it won't be fair for the roms makers