The last few firesides, it was mentioned that some Alliance guns will likely make it to Skirmish. The gas mortar, never. Cav rail gun would have to have some extreme changes, so not likely to see Skirmish.
The ships were not entirely ruled out, but don't expect to see them in Skirmish any time soon. Even if they were added, you would still likely need to unlock them in Alliance first since they are DLC content. If you have devapp, you can check out all the new Alliance things, plus two new Skirmish maps ported from Alliance.
As far as how balanced the ships are, once again, show up this weekend for devapp testing. Something special is planned.