It doesn't really surprise me, although I think there's going to be a lot of resistance to it. If he ever went to completely subscriber content, I think you'd see Newscorp lose market share to those sites that continued to be free. The only way that this works is if all the major news sites do something similar.
That being said, I think it's possible to charge for selected subscriber content. Look at the case of ESPN, which seems to be moving along fine with Insider.