Scientists, including New Horizons principal investigator Alan Stern, met in Houston on April 24th to discuss the possibility of a Pluto orbiter mission [scientificamerican.com]. The mission would likely cost $1-2 billion, compared to around $700 million for New Horizons [wikipedia.org] and $467 million for the Dawn mission [wikipedia.org] to Vesta and Ceres. A launch date in the late 2020s is possible, with a 2030 launch coinciding with the 100th anniversary of Pluto's discovery:
[A] Pluto orbiter mission is a long way from becoming reality, Stern stressed. He said he and his fellow researchers aim to mature the concept in time for it to be considered during the next Planetary Science Decadal Survey, a U.S. National Research Council effort that sets exploration priorities for NASA every 10 years. The next decadal survey will start in 2020, finish in 2022 and be published in 2023, Stern said.
Using the Space Launch System (SLS) could reduce travel time [spaceflightinsider.com] compared to the nine-and-half-year journey of New Horizons, but braking would be required to orbit the Pluto-Charon system, increasing the total travel time back to around seven to nine years. Other missions being considered include flybys of more distant Kuiper Belt dwarf planets [wikipedia.org] (Eris, Sedna, etc.) and exploration of Neptune's moons Triton [wikipedia.org] and Nereid [wikipedia.org], which are likely captured Kuiper Belt Objects. Triton has about a 14% larger radius and 64% more mass than Pluto. Voyager 2 observed 40% of Triton's surface in 1989.