They're working their butts off on Civ VI, but it won't be announced until they've milked Civ BE for as much money as possible and its actually close to being done. If its not better than Civ V, they will feel it in the bank account pretty hard, but that is a matter of opinion anyways.
I'd love it if they changed the military to creating armies instead of units, and brought back the ability to create a big ol' stack of death like the old days. Instead of military units, with one purpose, an army would be created instead and production would be used to strengthen aspects of it. A full city smashing stack of death could be created using tons of production and gold, with each section of the army being strengthened by what the city decided to work on that turn. The effects would be the same as now, but the change would give us so much more control and make things far more realistic. The army can of course be split into platoons, with management down to the last man as to how strong you want each platoon to be. I'm sure they can multiply the combat shown in Civ 4-5-BE to show thousands of little dudes crushing each other on the map in the space of a couple tiles. And as for the 1 mile per year rate of army travel, that is preposterous. This absolutely should be cleaned up to maybe be army defense range or end of turn targets instead of moving either 1 or 2 tiles every 100 years like this game does. Tile tactics are great, but 1 unit per tile is silly.
I'd also rather it not take 1000 years to build one stinking library, and instead have it be more realistic and work on building realistic infrastructure. Like a darn library on every street corner after 30 years of work! Wonders could also be changed so that they are ONLY built by great people, instead of us wasting our time building and building to lose it to someone on the last turn. The effects and the creation of buildings would not change from normal Civ, but it would make city management better since you could see immediate, albeit ridiculously small, results. There is no need to go to sim city style city management, as just choosing libraries for a couple turns would automatically place them throughout the city. But it would be cool to see the awesome city you were leading build itself up by focusing production/Gold on certain buildings to build throughout its range. A brand new city view screen or allowing super-zoom would be amazing in this game as well.
Other than that, I love the meat and potatoes of Civ, which is population growth, researching technologies, and managing the areas around a city that the population works. Whatever they change with that, I am fine with, as it is close enough now to reality to make me happy.
I also have not played Civ BE yet, and from what I have heard there is nothing I want from that game at all.