I suspect that when the polished Changeling gets released, the shapechange will be defined in purely cosmetic, skin-level "disguise self" types of terms, and that you gain no physical features or abilities that come with your new form. No flying, no swimming, no additional perception or breathing types, etc. And were I to have a player select changeling for their PC, that's also pretty much how I would rule that ability of theirs right now.
Their skin is malleable and can change color and stretch... but their actual physical body on the whole (inside and out) doesn't morph.
Yeah. This is my read on the intent based on the various twitter exchanges. You keep all your game stats, presumably all your physical limitations as well. Sure, you look like you have wings, but you can't actually fly.
Which will be really embarrassing when you are using your disguise to try to pick up Aarakocra at the local fly bar.
AD