In general, in private flying, nobody prescribes what navigation method should be used.
Although legally you may be right, I'm pretty sure that during IMC *training*, the instructor would not appreciate you pulling out the iPad (or any portable device for that matter) and use that as your primary nagivation device. Or secondary/backup device for that matter.
BTW the built in Ipad2 GPS is rubbish. I have flown with mine and it is quite capable of losing the GPS fix anytime during a flight. You need an external GPS.
Never had a problem with mine so far (Robin DR400 and R2160, both with perspex bubble canopies; no experience with PA28s or other metal-roofed aircraft). But anyway, even the 3G version,
AFAIK, can be paired with a separate GPS if necessary.