I'm going to argue that I'd prefer Pokemon not to be in USF specifically because of events like Horror Nights. Diagon Alley works enough because its enclosed from all other lands, which means the flow still somewhat works and is free of disruption. I always disliked that Simpsons land (besides a couple of things recently) remains mostly normal during these events.
I know Horror Nights is only a couple of months throughout a year, but I'd love to see them bring ideas to USF that still allows them to fully utilize each land during events. Heck, if Fan Fest grows to Orlando, you could utilize the space for those events as well. I think there are enough interesting IPs that Universal has at its disposal where you can make sure the park still gets full utilization during the events.
Which leads me to my main point: I'd love for USF to remain an events park and consistently have different "festivals" each month. Mardi Gras, Horror Nights, Christmas, maybe eventually Fan Fest could fill up the calendar.