There is actually a limit to the size of the stomach. The exact size is specified in the swallow whole description.
You are correct that things brought into the stomach via swallow whole are not subject to destruction such as items devoured.
Eat yourself is rather similar to strange movement. It could just be specified that if you have swallow whole you can enter your stomach instead, and if you do each minute rather than round counts as 5' or movement. Could also be an augment.
Though if you did so no new air would be coming in.
I'll think about the stomach feature. Mainly as I had a thought of an ozodrin pretending to be a building at one point.
Also, I just had a thought of, upon figuring out that a place was about to explode/implode/whatever, an ozodrin shouting to the party and any refugees to get in his belly, then doing so himself to avoid the blast.