It's important to remember that this only applies to content on the Oculus Store – you can still run apps downloaded elsewhere. It's primarily just a publicity thing – if they allowed adult content, they'd have to make a separate section for it, and the media would have a field day going through it. This way, they don't have to worry about that, and you can still download anything elsewhere.
That depends... I don't know too much about the platform itself, but if the OS is designed more like that of a game console, then they may be the type of asshole that actively discourages homebrew software development, charge thousands of dollars for SDK's, and push updates that intentionally brick your headset if you soft-modded it (see: Nintendo).
They have specifically stated that it will remain open – VR headsets should be more like a computer monitor than a games console. The SDK is freely available.