If a Hopper is $7.00 a month and a Joey is $7.00 a month and Hoppers can share what is on each others hard drives why would you lease any Joeys?
Four Hoppers would not provide any additional TV outputs than a two Hopper/two Joey system so a four Hopper system would be about additional tuners. To me, 6 tuners sounds like a lot but I'm not as much of a TV junkie as some on this site.
Billing issues aside, tech issues:
The modern dishes only provide 3 dual-tuner outputs (6 tuners) and all would be required for two Hoppers. You'd need to add two DPP44s to the system to provide the 6 dual-tuner feeds required for four Hoppers.
There isn't a "quad node" at least that we know of. Someone speculated you could interconnect two dual nodes using MoCA ports but no one knows if that would work. So you may not be able to share content across all four Hoppers.
All speculation at this point until people get systems in their hands and start pushing the envelope.