The planetary region of the solar system appears to end at a distance of about 50 AU from the sun at the edge of the classical Kuiper belt. Many high eccentricity objects from the planetary region -- comets and scattered Kuiper belt objects -- cross this boundry, but all have perihelia well within the planetary region. Far beyond this region lies the realm of comets, which are hypothesized to be stored at distances of ~104 AU in the Oort cloud. Every object known to exist in the solar system has either a perihelion in the planetary region, an aphelion in the Oort cloud region, or both.
A population between the outer edge of the Kuiper belt and the inner edge of the Oort cloud would be difficult to study. Objects in it would be distant, slowly moving, and faint. Study of this population would seem to need to wait until the next generation of survey telescopes. Nonetheless Pluto, the first body detected in the Kuiper belt, was discovered long before the technology existed to survey the smaller members of the Kuiper belt population. Similarly large bodies in the distant solar system can provide an early window into this otherwise inaccessible population.