Familiar features may pop up even in long-range pre-encounter views of Pluto. For example, New Horizons will be able to precisely measure Pluto's diameter. If the planet were slightly oblate it would be evidence for a solidified frozen "bulge," left over from when Pluto spun more rapidly. If Pluto still has a liquid mantle, material would still flow, reducing the size of the bulge.
If New Horizons imaging reveals a world covered with a crazyquilt "chaotic terrain" of the Europa-type surface fractures, then it would be evidence that an ocean existed at some point. Pluto might also be covered with dead cryovolcanoes that were produced when liquid from the ocean forced its way to the surface. However, the discovery of still-active geysers on the planet would be an eye-popper, and unequivocal evidence for a subterranean ocean.
Regardless, I have no doubt that New Horizons will uncover an extraordinarily complex Plutonian landscape. To date, the best of the Hubble Space Telescope pictures of Pluto show a remarkably variegated surface with of bright and dark regions, some of it molasses colored from photochemical effects from the sun.
Ten weeks out from closest approach, the New Horizons probe's photographic resolution will exceed Hubble's. The entire planet will be photo-mapped. At closest approach, features as small as twice the length of a football field will be discernible on Pluto.
Unfortunately, half of the planet will be in darkness during the brief close encounter. Scientists will be left to speculate for decades what secrets the unseen hemisphere might hold.
My prediction is that the images from the near encounter will leave astrogeologists with many more questions than answers about Pluto's history, internal structure, and dynamics. And, that's not to mention the chances of a subterranean ocean that is perhaps as illusory as the mythological river Styx in the Underworld.
Image credits: ESA, NASA