And by the way I don't think it's a crazy idea. I've been thinking about it for a while. I know how to program for the iPhone and I've been thinking about the same. This is the way I see it. it would be a system approach. A meter and note taking for the field, tied to developing charts on the studio and meter and stop-timer on the darkroom.
The meter on the field would be a hardware piece that would attach to the bottom of the iPhone with a real diode as to use as a spotmeter, and maybe another version with sphere for incident.
The program on the iPhone would receive the signals from the meter and everything else would happen on the phone. The advantage being that you could record everything and use the meter as a note taking device. I envision you could take the highlight and shadow measurements and the meter would run either zone or BTZS calculations and it would give you exposure as well as developing time all rolled into one based on your previous tests. Hit save and your whole session and picture data is saved for you to use when you get home.
When you get home. Look up the data for the picture you're developing and hook it up to a temperature probe. If you're using the BTZS tubes or developing on a tray the timer would run 6 timers at once and tell you when to get the tubes or sheets out to the stop and fixer.
Later another piece of hardware ( a relay that can run on USB connection) can run the enlarger. The software would do all the calculations based on the data from the exposure or just from the metering using the hardware piece that you use previously for metering on the field. The application would switch to enlarger mode and you could do all the things you can do with current f-stop timers but you could also add and program steps with much more ease that you currently can. It would not be easy, and it would require two pieces of hardware. Alternatively you could try to do it with the current camera but you might have to give up accuracy for convenience. Perhaps the hardware pieces are the PRO bundle, but you can get the software as the beginner version.
Just thinking.