People with Down syndrome are not flying planes across the globe to hang out over pu-erh and discuss the finer points of Western culture in a language all their own.
Aside from funding hurdles, this potential mission and others like it will depend on a steady supply of Pu-238 for propulsion and to power its onboard systems.
Given a start with some other fissile material (U-233, U-235 or Pu-239) as a driver, a breeding cycle similar to but more efficient than that with U-238 and plutonium (in normal, slow neutron reactors) can be set up. (The driver fuels provide all the neutrons initially, but are progressively supplemented by U-233 as it forms from the thorium.) However, there are also features of the neutron economy which counter this advantage.