They can't exactly keep querying players' ilevels as it would probably lag the dungeon to Hell. What they should look at though is an ilevel verification if gear is swapped at any point. It would probably create a small delay when you swap for the processing time but that's fine. If you would fall below min ilevel you would get a red message saying you can't complete that swap. They could also implement an absolute minimum ilevel for individual peices of gear. Set it 10 or so levels below the min average for the dungeon.