What do you have in mind?
Pretty much the same idea you had (replace it with a battlescape fight), since this would be the easiest to implement if you are looking for a total departure from the current mechanic. But i had to reject it for the reasons i listed - it's not a true change or a new mechanic - it's just more of the same that's already in the game. The problem is that battlescape is designed for squad-based ground combat - not for aerial dogfights. My ideal choice would be something like X-Com Interceptor or a true dogfight simulation - neither of which is realistic, given the contraints of openxcom.
Something i completely forgot to mention is how additonal equipment slots would be handled. OCXE adds the ability to use up to four weapon/equipment slots, while soldiers in battlescape can use a max of two weapons. How would this be handled? Do we need to redefine crafts and craft weapons? How would this be compatible with vanilla dogfights?
A close range shootout between 2 units won't last long either.
True, but it would still be bound to battlescape rules&mechanics, meaning multiple turns, intro, exit and possible equipment screens.
I do have ideas how to vary the outcome (see below), but didn't put them in the first post to encourage people to suggest something less obvious[...]
Clouds or other obstacles were also on my mind regarding tactical options, but again, this would be like having a total flat battlescape, with the addition that you get to use smoke grenades.
You can't see this as a totally separate game mechanic - you're prefacing a 'real' tactical engagement with an inferior one. Would you want to play through this hundreds of times? I don't think i would. I would probably try it a couple of times and then disable it. I just can't think of a way to make these as engaging as the ground assaults - and they would have to be in my opinion, otherwise you're just adding a ton of mandatory knock-off battles to the game.
And, as mentioned above, you run into problems with changes that have been made to the vanilla mechanic. It's simply not as easy adding an 'optional' combat stage to the game. You can't reuse existing content - it would need to be designed from the ground up to support that mechanic
and vanilla dogfights, and it would need to be balanced for both modes for it to be 'optional'.
Would it be possible to implement? Probably, since it's reusing elements already in place. But would it be a worthwhile addition and would it be justifiable to rework existing and future content to support both modes? How much work would you have to put into it to make it interesting and different enough from ground battles? Would it even be possible to do that, given current and future limitiations and extension to ground-based battlescape gameplay?