"Will some SDK-developed Apps cost additional money?" I think that's a no-brainer: Of course they will.
I think some more interesting questions, to which we have no clear answer yet, are:
- Will there be any mechanism, if individual developers choose, to distribute some of the SDK-developed Apps free of charge?
- How much editorial independence will the developers have to cede to Apple in exchange for digital signatures or distribution rights?
- How effective will the sandboxing be at preventing one App from maliciously damaging or harvesting the private information that belongs to another App?
- What potential software capabilities will have to be sacrificed to achieve that level of protection?
- Will there be options available to remove some of those restrictions to allow more powerful applications, in the cases of trusted developers? What would constitute a trusted developer?