Would something like this be useful if it showed common repair issues? Like top-10 or top-20 repair how-to's?

I suppose it could, in the same way a reference manual is useful. I personally find stuff like that (virtual interactivity) less than useful, as it takes several viewings or constant reference back to absorb everything you need to know to move quickly through something.

It would also have to be a strictly offline thing, since if you have internet, you have youtube.

My personal experience walking someone through various and sundry repairs without helping has been wildly variable. Mechanical aptitude is more than just the adjustment or repair procedure; you may be surprised to have to tell someone something as simple as 'screws generally tighten/advance by turning clockwise'.

For an example of how in depth you would be shooting for, search for 'Shimano S-tec" and watch a sample video--all necessary tools for the procedure are laid out, and any time a bolt/screw is turned, the tool used is identified. Telling someone the procedure to adjust a derailleur, for instance, it's easy enough to say, "you need a screwdriver to adjust the limit bolts." But they may also need a 4 or 5mm hex key for the pinch bolt (or a t25 torx, or a 9mm wrench...). Campagnolo derailleur limit screws are difficult to impossible to engage with a #2 Phillips...Shimano and SRAM are not. Some derailleurs don't use screwdrivers for limit screws, but use hex keys. Some derailleurs do not have adjustable tension ("B tension")...Such minutiae are why a company-sponsored training manual (or app) can work well, but not apply to everything.

only if it's as good or better than this (which I can easily access from mobile devices)

Repair Help Articles | Park Tool

And for most jobs I haven't done several times I want to see detailed videos which are pretty much covered on youtube

https://www.youtube.com/user/wwwartscyclerycom

https://www.youtube.com/channel/UCuT...OkJ0H_GAztWt0Q

I downloaded an app like this once. I used it twice before I figured out that working on bikes is simple and I never needed it again. It's not hard to learn the simple things, adjusting derailleurs and what not. What most people need a reference for is the ODD things, like "How the hell do I remove a cannondale headshok fork from the headset...?"