I called Chase and got the straight poop on this. Because of the airline merger, Chase is renaming the card from Presidential Plus to OnePass Plus. (Chase did not specifically confirm what I'm about to say, but one assumes Chase is removing the word "presidential" because Presidents Clubs won't be called that after the merger.)
In any case, no features of the card will be changing with this renaming/reissuing, however, it is known that "new" features—not necessarily associated with this renaming—are in the works. One interesting new feature is that cards will be "laser engraved" with the cardholder's signature prior to being sent to the cardholder. (This is a security feature which Chase may incorporate into other cards as well.)
One further assumes the Presidential Plus MasterCard and Mileage Plus Club Visa will merge into a common card with whatever new features are coming. This however, may have to wait until OnePass and Mileage Plus combine, and that, as my Chase banker told me, is not going to happen soon after merger. That is, Chase has been told OP and M+ will operate separately at least for a while.
Finally, Chase renaming/reissuing the PP card so long before possible regulatory approval, seems to indicate it is confident the merger will go through. ^
Who at Chase did you speak to? Was this all from your banker? Based on your post I just called Presidential Plus customer service and they did not say anything remotely similar to your post. Also I recently received a letter about my card but it didn't refer at all to a "OnePass Plus" card.