I don't think they'll need new receiver hardware for DSWM, all or certainly most of the current SWM-capable receivers should work fine. HEVC decoder chips run hot and expensive today, but there are so few people with 4K TVs yet there isn't any rush to push out a 4K receiver. I wouldn't look for it until D15 is launched and in position.
There's no way they'll "standardize" on 4K capable hardware for a long time. They don't even standardize on HD capable hardware today! HD capable hardware is far more useful because almost all the channels anyone watches are available in HD. That may never be true for 4K, or at least not for a very very very long time.
4K will be a Directv advantage over cable, since it'll be difficult for cable to offer more than a few token channels unless they really go heavily in SDV. But the early adopters of 4K will have to be willing to pay for it, they aren't going to get it as a freebie offer like Genies and lifetime HD are handed out today. Why should Directv do that, when they'll be the only option to get 4K for a lot of people aside from Blu Ray?
The third generation in the patents might require new hardware for the dswim system should they go that far. And really, at this point, any hardware they put in a next generation of receivers should be strong enough to be able to decode anything of high res, so that they can tweak it to work with whatever schemes come along for the foreseeable future.