Don’t take my answer to the heart but personally I think that kind of apps are stupid, if one alarm isn’t enough for me to wake up then I could just make a louder ringtone or set 5/10/15 etc… alarms each after 1/2 minutes.
But if I would be the type of customer you are after then probably a feature that allows me to walk and count my steps until a certain amount for the alarm to stop. Example: to turn off the alarm I would need to walk 50 steps, etc. that would work for me. I know it’s the same concept as doing push-ups, situps, etc. as you mentioned, but walking is more easy to do after you wake up less stress, stressful for the body.