We know there are dragons. And we have screenshots of said dragons which wings. If they have wings for purely cosmetic reasons, I and most people will be extremely disappointed. Therefore I think it's pretty safe to assume that there will be flying units in the game.
We do know there'll be dragons, but in the tactical screenshots that have thus far been released they haven't been flying. At this point it still seems conceivable to me that they may have movement bonuses on the strategic map to reflect their ability to fly but act as solely ground based units on the tactical map. Like I said before I of course hope that's not the case, I'm just erring on the side of caution until we actually get anything confirmed.
Thankfully, there has been a lot of headway in tactical combat in the 15 years since MoM. For example they can just coopt HoMM's system of dealing with flying units. Just let flying units fly to any open spot within range, regardless of obstacles. There are lots of ways of determining what types of attacks can affect flying units, too. They could do it HoMM's way (anybody can hit them anytime), MoM's way, or even another way. For example 'flight' could be a toggle ability; while flying units are in flight they can't attack (or maybe could only do significantly weaker-than-normal strafing attacks), but can only be hit by ranged/magic attacks. And if flying units are currently grounded, they'll deal their full damage but can also be attacked by anybody. Stardock has lots of good options to handle flying units - choosing which to use will be the hard part.
Well I'll bow to your superior knowledge as now that I think about it I can't recall playing any 4x games with tactical combat since MoM.. other than the Total War games which obviously don't include flying units. The above suggested systems do sound pretty workable so lets hope one of them, or something even more exciting will be applied in this case.
On a side point, as I've only ever played Gal Civ 2 that's been made by Stardock, have they previously made any games involving tactical combat? Do we have any idea how in depth they're likely to go with this aspect/how much of their development resources they're likely to commit to it if they don't have any prior experience?
Naval combat is especially difficult because of how boats move, and how units onboard the boats affect the battle. I don't think cannons are going to be common (or even exist at all) in Elemental. That means destroying other ships would require ramming, setting them on fire, or boarding them.
Yeah I guess you're right, I was more thinking of a paired down version of naval combat with the more abstracted interface of MoM where each vessel just acts as an individual unit with the contained units playing no part at all. I still think that's potentially fairly easy to implement on a very simplified level but I do concede that if you want to take into account boarding, realistic ship movement (tacking etc), as well as incorporating the onboard units then the complexity does ramp up exponentially. I guess if Stardock aren't happy with such a simplified system then that probably augers well for their treatment of the land based tactical comabt eh? 
