MPO images, as you may know, are pretty much concatenated JPEGs. So though they don't take up nearly as much space as other formats like PNG, a lot of them can add up. As with the photo uploader idea, 3D photos can just be uploaded to an image hosting website like Photobucket (which does support MPO), and with the 3DS browser, this shouldn't be a problem.
@Takis Teh Greek I know what you're saying. But rather than to allow uploads (which would be quite a step), perhaps allow users to display their 3D photos. However, even with administration, personal content/consent/privacy would be quite an issue.