Dish doesn't charge current subscribers any fees for "sling" access to their live or DVR'd content. The apps are free, website access is free, and the Sling device is either built in to the receiver or available for a nominal, one-time fee (they were even giving them away at one point). Why do you think they'll change their policy on this in the future? Seems to me that it would be a value add that would help gain and retain subscribers.
I know most on this forum don't like Ergen and Dish. I do agree that I think the Softbank deal makes more sense, but I am also intrigued by the possibilities of a combination with Dish just because of all the excess spectrum that will be available. BTIG research has been saying that Sprint/Softbank need to hurry if they want to close a deal because Dish may be hunting for a cash-rich partner to help them in their bid. If Dish is able to find a cash-rich partner, the one big downside of their deal (the huge debt load) would no longer be a concern -- and that would make the Dish deal stronger than it currently looks. Of course, that's all speculation, and right now the Softbank deal looks like the best strategically.
This is all so very interesting :-)