I doubt Nintendo will do a pure streaming service. I don't believe they are totally blind to the services that have yet to get off the ground or the ones that are closing down because not all markets can handle the network rigors needed for such a service. Square just ended their attempt to do such a service. Sony's is currently running but not really a big service that can stand on its own, or in other words support a dedicated machine that just runs streamed programs. And I do believe there will not be a time the US will be able to do a streaming service outside of a few metropolotian (my spell check currently isn't working) areas. Plus doing so will need a partner to run the servers through out the world since a service like that requires semi-local servers to help minimize lag. For a "simple" flash game just having one server farm on the east coast on the US isn't enough to prevent content lag. And Nintendo isn't a tech company like Microsoft or as far as our knowledge bought someone like Sony. The only one of their current business partners that have such resources would be IBM, and we whould of heard IBM boosting about scoring something like that even if they didn't say any names.
If they go this route I can see them doing a download service with some cloud/streaming capabilites were most of the game is downloaded, or installed via a cartridge and the rest is streamed/downloaded and then can be played. And looking at the way they handle their digital games on the eShop I can see them doing something like this.
