I'm pretty sure Rebellion was "Shipped" due to a lot of community outrage when we found out that Diplomacy was going to be the last expansion after being promised 3. Likely, Sins 2 is the next step, hopefully with some sort of campaign and the Vasari enemy...
Well, in any case Rebellion helped them making a lot of money so Sins 2 is likely. Although probably in the distant future.
A campaign would certainly be nice.
About the Vasari enemy I am not so sure..... that would mean a fourth faction..... and would be a nighmare to balance and nearly impossible to justify in lore.
I mean this unknown enemy crushed the ENTIRE Vasari Empire... it would effortlessly moop the floor with any other race.
For game purposes, the race has to be equal.... but then that brings up the point of why the Vasari are running at all.
I think it would be wiser to create a lore where all factions successfuly escaped our galaxy from the unknown threat and start over in ta new galaxy... and of course... you now humanity.. in time they will be at war again.
Or create some tremendous cataclysm that happened to wipe out the Vasari menance..... by lucky accident. So the Vasari no longer need to run.... and so the Vasari begin to rebuild their empire. But of course the other factions dislike that idea and as vasari expansion is usually expand explore conquer soon war rages again.