I think it will be some FF news, or plans to combine the two universes. I don't think X-4 will be on the table until next year earliest. Even then, the cast is getting older and I think DoFP will be the last hoorah of sorts if I had to guess. A sequel to DoFP set in the 80's seems more likely.
Unfortunately, the only deals I can see being worked out between the MCU and Fox are part time character loans and small side deals. I don't think the universes can be creatively combined until the rights revert. So I think we may see Silver Surfer in the MCU while the rights are still at Fox. Or Black Panther with Fox.
What's the easiest way to get these characters exposure? By introducing them in established franchises. BP by himself will probably flop. SS movie is risky considering the budget it needs.
Another unlikely but plausible possibility, the Fox universe could acknowledge events in the MCU and vice versa, so while we may not get cameos, we can get small easter eggs here and there.
However, if Fox intends to combine X-Men and FF together, I think there is enough there for a cohesive universe, and they will work with whatever they have. MCU will not be a part of it in any way. I don't think Marvel/Disney cares about combining mutants into their world. Cosmic beings like Galactuc and SS are a much higher priority, so much so that they were willing to forgo rights for Dare Devil.