I don't think they'll look at HBO Now as much competition to having it as part of your programming package with DirecTV. I expect there will not be any reduction in price, but hopefully this will slow down the price increases on HBO.
I don't know of any time where DirecTV has lowered pricing due to something new coming to market. Streaming specific, MLB Extra Innings vs. MLB.TV is a good example. EI is $70 more than .tv, and has been for 10 years. They did lower the price about $20 a few years ago, but I think that is more related to price point pressure as they pushing the $220 mark.