Aside from propulsion, which is solved at least for space probes, the great problem of outer-planet exploration is bandwidth. Using a microwave high-gain antenna, the data rate at Saturn is on the order of 10kbits/s and New Horizons would have to cope with 1kbit/s at Pluto. This is incredibly small for instruments capable of taking high resolution pictures.

So the next revolution in space exploration would have to tackle the data problem; optical or near-optical lasers for transmitters and standard photosensors (CCD) for receivers. It is technically possible to use off-the-shelf components, the remaining difficulty being the beam aiming system.