Currently, I honestly think that the best course of action for Chase here is to raise the annual fee by $100 and add United Club access (contingent on their co-brand negotiations with UA). If they can pay a similar per-visit amount to UA as to Priority Pass, this will likely end up a wash, and it will make the card feel higher quality than every other card that offers a Priority Pass membership, since the value proposition of Priority Pass (and perception as a premium product) seems to have been severely diluted due to the number of cards that now offer it.
This is not realistic. As was recently published in multiple news articles, United is already unhappy about Chase branded cards eating into their cobranded card revenue. Plus Chase already has the MP club card with a $450 annual fee, why would they give away United club access for $100?