The rumor is they will not sell APs that include Epic Universe at first.
When the time comes for Epic Universe AP previews before the park grand opens I’m sure anyone with the appropriate 2 or 3-park passes would be able to experience a preview. Those are the passes you can buy now.
They would not be not blocking AP passes. They would just not sell them for Epic Universe to start, again, according to a rumor.
If you’d want to visit beyond the AP previews but before you can upgrade/purchase an AP that includes Epic Universe, you’d probably have to purchase a day ticket. That’s the rumor.