I was researching RTGs (Radioisotope Thermoelectric Generators) and after reading this chart... I realized something... Could you theoretically make a mixed-oxide or even breeder RTG? After all, they're basically solid-state nuclear reactors that function on passive decay... So, perhaps you can mix together different isotopes together into a form of MOX RTG fuel to balance out the lifespans and power densities of the various fuel isotopes. Perhaps you could even put some neutron reflectors into your RTG to make it a kind of hybrid of an RTG and proper reactor, the neutron reflectors speeding up the burn rate of the fuel isotopes, or perhaps you can even mix fertile isotopes like thorium or uranium into the RTG fuel to improve lifespan, as the neutron flux in the RTG could synthesize more fuel for itself as it burns?

7628635
RTGs have the ultimate weakness that the radioisotope will eventually wear down the generator. A breeder design would only make it wear faster.

7628810
True