I've started thinking this is not as simple as Netflix just not allowing it. I spoke with someone from Netflix for an interview (it was focused on their increased development of original programming, cord cutters, etc.) and off the record, he said Netflix would LOVE to be native on all the 4K Joeys because that just increases Netflix viewers, how in spite of how easy it is to get Netflix on tablets, phones, smart TVs, etc. every time they have a popular device get native Netflix capability they get a big spike in their viewing numbers, and so on.
I don't know, but perhaps Dish is saying Netflix is the holdup and Netflix is telling Dish, hey you need to do this or that so it will work? It's been long enough that the whole argument that it's takes a while to get an app ported to a new device and the 4K Joey is different from the regular Joey or Hopper doesn't sound plausible any longer. In all of this time a LOT of new devices have come out with native Netflix apps.