Earlier than that

1982 is the year Penn State came up for a membership vote in the Big East. The Big East actually voted 5-3 in favor of admitting Penn State, but a 2/3 vote for admission was required, so it failed.

Because of the secrecy of the vote, we'll never know how/why that happened, but a few theories have surfaced. It's been rumored that Boeheim didn't want Penn State in the Big East. OTOH, it's also been rumored that the three dissenting votes were cast by Georgetown, Villanova and St. John's. Not defending Boeheim, but I think the latter possibility is more plausible -- those schools likely would have seen Penn State as less institutionally/athletically compatible, perhaps irreconcilably so.

In any event, this spawned Mike Tranghese's memorable comment that "We will rue the day" when we denied Penn State admission. It took 30 years to completely come true, but Tranghese certainly was right.

Hard to imagine how different the landscape would look today if the Big East had taken Penn State back then. I don't think the Big East would have added football immediately, but it would have happened sooner than it did. And a Big East with Penn State certainly would have been a stronger football conference than a pre-Florida State ACC.