I think we need a continuous stream of Voyagers. Each with the latest sensor suite but otherwise using proven designs. What could we learn with, say, a good telescope mounted to one of these. It’s also not out of the range of possibilities to have a high bandwidth telecommunications infrastructure deployed across the entire solar system.
You need more broadcast power the further you’re away from earth and there’s less solar energy per m² the further you’re away from the sun (Neptune is 30 AU away, so there, per m² it’s about a thousandth of what we get around earth), and launching nuclear powered space probes (let alone a continuous stream of them) is a bit controversial.
You also would need a lot of large radio antennas on/around earth if you want to receive from these probes 24h/day (and if you don’t, you of course give up effective bandwidth)
I wonder what it would cost to build an exact replica of a Voyager and launch it on one of the newer launch vehicles? Obviously, we're not going to get a gravity slingshot off multiple gas giants, but considering that Voyagers were launched using Titan rockets, we should be able to give it a much better push from Earth orbit.
"Having expended almost every bit of the rocket propellant it carried to Saturn, operators deliberately plunged Cassini into the planet to ensure Saturn's moons remain pristine for future exploration"
A series of relays spread across the Jovian orbit would be an interesting way to mitigate the effects of the inverse square law on transmissions from extra-solar probes.
