Regarding 4K (and to add to what's been said already):
If you decide to get 4K from DirecTV, be aware that, aside from additional hardware (such as a specially-required Genie mini for 4K), you'll have to subscribe to the most expensive programming package as well. A back-of-the-napkin calculation could see you spending between $30 - $40 more on top of what you might already be spending in order to be set up for 4K. And as I've already opined many times, you need to decide if the relative lack of 4K programming relative to all other programming is worth that to you.
Otherwise, upgrade eligibility is typically determined either by being off contract or having your account set to where you can upgrade to a Genie for next to nothing. I say, "next to nothing," because when we went the wireless Genie mini route (which is a really nice way to get TV), DirecTV charged us $99 to have the wireless video bridge professionally installed.
At any rate, if you do upgrade to a Genie DVR, you'll have the "back end" of your wiring similarly upgraded (if not already) to the SWiM system (I'll let you Google that to understand what that means). Essentially, physical coaxial cables do not determine the number of receivers you have; "channels" multiplexed do, so that a Genie DVR (of any sort) has 5 receivers but only one physical coaxial cable. And an HD DVR counts as 2. Minis are slaves to the Genie DVR, so they don't count, per se.
If you decided to replace any of your current receivers (especially if they're non-SWiM-compliant) with any sort of Genie mini, be aware that you'll want to have at least one other HD DVR on your account, because if the Genie DVR fails, your minis will all fail, too.
