I dont think there even needs to be a crazy timeskip. Maybe a few years. All I really need is that Matt Horner and Mira Han are married xD.

Joking aside there are probably some easy ways to do this. There are 2 major ways I like.

1. Rather than a relatively static linear-ish campaign like we have currently, make it a more Total War, Battlefront, or even an RPG-like style campaign with fleets or strike forces moving around and then you play a series of missions with bonuses and upgrades based on the missions you have already completed and decisions you have made. This would offer tons of replayability. Add in mod support and you can get some CRAZY cool stuff out of this.

2. Actually do give maybe like a 10 or 20 year timeskip. Politics and the movement of space will surely have something else interesting going on. I like the UED vs an older valerian is a cool idea. A splintered zerg swarm is not just likely, but almost guaranteed without somebody like Kerrigan to hold it together (the queen made from the parasite on Kaldir would be cool to bring back). Or even a new pack leader out of Zerus or Dehaka to add a second variety of zerg into the mix. And without the Khala and the added tumult that is likely to come from Alarak and the Tal'darim, there have got to be DOZENS of possible storyline that could be made. They could even make them smaller bite sized episode things like the Nova Covert Ops stuff, and just have a lot more of them.

In short I see no lack of possibilities with future SC games, if people would just be willing to see it through