Universal has no actual incentive to let AP holders flood their new park, especially AP holders who did not pay for access to a theme park that was not included in the AP agreement in the first place. Universal’s preference is to maximize profits when the park is at its newest, which means limiting free admission beyond what is necessary.
I don’t foresee Universal granting APs access to Epic beyond the barest minimum simply to say they did. Universal knows people will want to attend Epic in its first year. So Universal will make as many people as possible, including APs, pay for the honor.