Phil of the Future/WMG

Lloyd and Barbara's marriage is doomed to collapse

As seen in the episode Time Release Capsule, just after they started dating, they found amazing stuff in the time capsule. If they hadn't found the time capsule, then they would have gone their separate ways and forgotten about each other. Because they did find the time capsule, they couldn't bear to fight over the expensive objects inside.

Their marriage is built on material goods. This is usually a sign of a not-so-healthy relationship. Ergo, there will eventually be a bitter feud and, ultimately, a split.

The Diffys stayed in the 21st Century when they turned around for Curtis

As seen in the episode Back To The Future (Not The Movie), the Diffys turned around for Curtis. Word of God says they would have stayed in the 21st Century.

Phil becomes his own ancestor...

Which thus leads to the end of the pinky toe, causing a double Stable Time Loop.

Phil and Keely get married

Which probably messes up the Timey-Wimey Ball but who cares, Word of God says they ended up together. Those Time Police will go nuts.

Phil was a Time Lord.

Yes, it's tiresomely predictable, but here is actual proof!