Directv doesn't have any incentive to move people off satellite. It doesn't save them any money once customers are installed, and could cost them money if they price the 'Directv via IP' product lower (though based on the packages shown as being available for Directv Now, it looks like the pricing will be the same modulo no "advanced receiver fee" since there's no Genie)
What I think they will do, quite quickly after the Directv via IP product is available, is to preferentially sell that new customers because of the savings in install costs that Directv would normally eat. They might even start charging for new installs of satellite as a way to further incent people to go with the cheaper-to-install product.
What you're saying makes sense, and I see those as steps to be taken starting in 2019/20, not five years from now. A little lower overall pricing (installation + equipment + programming) for streaming vs. satellite, along with a stronger marketing push for the former, will do a lot to shift the distribution mix over the course of a few years.
Only thing I'd add is not to read too much into the pricing that AT&T posted a week or two ago for the Entertainment, Choice, Xtra, etc. packages on DTV Now. I'm not sure what their rationale is in putting those packages on DTV Now at those prices but I don't believe it's a key part of any long-term strategy. That may or may not be a guide to how pricing for their forthcoming "DTV over IP" will compare to traditional DTV satellite service.