This sounds to be a weird question, but I would like my App not to support iPhone 5 layout at this moment.
I know, to support iPhone 5 layout, I have to add a Default-568h@2x.png as Launch Image, then the XIB will be resized and supports iPhone 5.
The current issue is, the layout we currently have does not have iPhone 5 4-inch layout. If iPhone 5 4-inch layout is enabled, the buttons are disabled. After discussed with co-workers, we decide not to support iPhone 5 layout at this moment, i.e. we prefer to leave black borders on top & bottom of the App. Is it possible to submit an App without Default-568h@2x.png ?
Yes, that's possible. The Default-568h@2x.png is just a flag to trigger iPhone 5 support and we've successfully submitted fixes to Apps without adding the Default-568h@2x.png file. Apple will currently not reject your App update for not supporting iPhone 5.
Of course you should update the App over time and I would not be surprised that Apple will change this policy in the future, especially for new Apps. But for now you're okay!