I imagine a lot of this in Orlando (and SoCal, frankly) is cyclical, yeah? A family might have Disney passes for a couple years, drop those and then move to Universal for a couple years and so on and so on. So while it wouldn't surprise me to see the number of Universal APs drop, I don't see any reason to think that's permanent. Give Epic a little more time to improve its reliability and by the time they add a new attraction, perhaps they'll feel comfortable adding it to annual passes.
Myself, I'm fine with IOA and USF for AP, as long as there's no big price hike. I enjoy vacationing on site at the North Campus, and
probably wouldn't do Epic more than once or twice over a long vacation anyway. And, as a tourist that takes long vacations at Universal, the
AP hotel rates are more important to me than Epic. I'm comfortable staying on site and not having to travel to parks, like at WDW. But
I'm probably a small minority. Universal had a large increase in AP's the last few years, and most of that was probably in anticipation
of Epic, and was probably largely locals. Those are the ones that will probably let their passes expire. Some of the long time local AP's
might stay, some will leave. But I doubt they'll get more than a small amount of new AP's.
Bottom line though, I think they'll lose a significant number of APH once their passes expire. If Universal would have built the park with adequate
capacity, none of this would be necessary.