The way I see it you should treat it like any other UX problem: The user is going to be at home anyways, so if you can get a "conversion" (even a short 7-minute one) that can easily bridge them into the next step. Just like video games start you off in tutorial levels and help you develop the skills you need (e.g. Mega Man X [1]).
For example I tried out the 7-minute exercise simply because I could, it was easy. If I can't even be bothered to spend 7 minutes on exercise there's no way I'm going to the gym, so it's not as if the short exercises are interfering with work at the gym.
The problem with bodyweight training is that there's no smooth gradient from wall sits to, say, pistol squats. The difficulty increases lumpily and frequently requires a new motor pattern to be learnt.
Whereas going from a 20kg squat to a 100kg squat can be done 1kg at a time with the same movement pattern throughout.
For people who genuinely can't or won't go to a gym, I'd first suggest installing a power cage, adjustable bench, barbell and some plates. Failing that kettlebells and resistance bands. Only after those are exhausted would I suggest a purely bodyweight training regimen.
For example I tried out the 7-minute exercise simply because I could, it was easy. If I can't even be bothered to spend 7 minutes on exercise there's no way I'm going to the gym, so it's not as if the short exercises are interfering with work at the gym.
[1] http://youtu.be/8FpigqfcvlM?t=5m53s