I think this dynamic is changing a little. With Iowa it'd be a lot more than 10% now with a younger demographic.
My friend's daughter is a grad assistant working in the ticket office, and she says they're converting TONS of season tickets into mobile pass customers, and gaining tons of new customers because they're so much cheaper. It's a situation where the old fogeys in the 55+ club still want their dedicated seats just like the want their paper tickets and landline phones. From conversation with her it sounds like a much larger block of mobile passes (more than double last year) are going to go on sale because they sell out fast.
The 20-50 crowd are wanting cheaper options and don't mind electronic tickets or sitting somewhere different each week. I love it. $275 vs. $500 for the exact same seating areas? Shiiiiiit, man.
Now one could argue, "hey, they'll just jack up the price of the mobile passes..." and you might be right. But like you said, interest is waning and the fogey crowd is dying off in a hurry. The remainder of folks ain't gonna pay $600 on up to a grand or more per seat anymore. They'll just stop coming to games. I know myself that if they get rid of the mobile pass I'll stop going except my once or twice a year trip with tix that I either scalp from buddies or get cheap off stub hub. Iowa isn't a Michigan where you're going to fill that thing with nothing but rich donors in perpetuity.