Oh, they'll definitely be pushing it. And many people will see "$15 a person a day", say they are spending enough on the trip, and ignore it.
I'm with
@CaptainAmerica here. Utilization is going to be significantly less than FP+.
For starters you'll have APs and CMs who go more regularly - they won't
never buy Genie+ but they are unlikely to do so on every time in especially if they go frequently. So, that's some percentage of the crowd (and they would typically be high FP+ utilizers). Next you have people who are just stretched too thin in terms of the cost - especially big families where that $15 per person adds up quick. Or they could afford it but don't think it is worth the costs. Maybe they buy it one or two days on their trip, but not every day. Then you have the non-tech savvy (moreso older folks) or people who don't want to look at a phone on vacation who will say phooey and just not want to partake because it would annoy them to use the app; that may also include some non-domestics who might not want to rely on wifi and would be afraid to purchase if it can't be used reliably. And you'll have some people who will purchase it - especially as an add on when booked for all their days - and then scantly use it or even not use it at all because they don't think about it. Those folks who technically be users but not really impact the availability or the lines. You'll have some people staying on property that will opt to use the Early Entry (and evening extra hours if in Deluxe/DVC) plus rope drop to get shorter lines rather than spend extra money.
I'm just skeptical of the people here who are saying "it's so cheap everyone will do it". A lot won't. Right now, I'd guess it will be closer to 50% of guests on a given day rather than something like 80%.