No, this is a bad idea for several reasons. It might be a good idea if there ever becomes a lot of spacecraft out there, but otherwise...
- The relative positions changes over time. One would need a number of these to work reliably, otherwise there's a good chance it just wouldn't work.
- Solar power doesn't work that far our. The current method to power spacecraft is radioactive decay. It looses efficiency over time, so the mission would be limited.
- Orbiting that far out is really difficult, and hasn't been done yet.
- The pointing of the antenna correctly would be more difficult. Basically pointing at the Sun points at the Earth when you are that far out, pointing at the nearest satellite is more difficult.
- If one of the satellites failed, you'd potentially lose the mission. Not really an option.
- If you are really far out there, it doesn't matter that much. Voyager's are both over 100 AU. Uranus is only 19. Hardly a scratch. Most spacecraft going out that far for the foreseeable future aren't going to stop, they will be at a solar escape velocity, and thus keep moving further with time.
Basically I think it'd only work if there was a lot of spacecraft out there. Maybe around 100, but no fewer than 30. That means you aren't quite as reliant, which should improve things somewhat. I can't see that happening for a long time.
Where this does work is if you have a number of spacecraft close together. Where does that happen? Mars. A Mars communication satellite has been discussed for a number of years, and in fact most Martian satellites double as communication relays after their primary mission is over, and to a lesser extent before their primary mission is over. It complicates the operations somewhat, but it does work.