I think the proliferation risks will be in future the reason, independent of technological obstacles or costs, why US will not allow to build fusion power plants in all countries around the world.
Hybrid nuclear fusion–fission power plants have been already proposed and studied in theory.
"In general terms, the hybrid is very similar in concept to the fast breeder reactor, which uses a compact high-energy fission core in place of the hybrid's fusion core. Another similar concept is the accelerator-driven subcritical reactor, which uses a particle accelerator to provide the neutrons instead of nuclear reactions."
Hybrid nuclear fusion–fission power plants have been already proposed and studied in theory.
"In general terms, the hybrid is very similar in concept to the fast breeder reactor, which uses a compact high-energy fission core in place of the hybrid's fusion core. Another similar concept is the accelerator-driven subcritical reactor, which uses a particle accelerator to provide the neutrons instead of nuclear reactions."
https://en.wikipedia.org/wiki/Nuclear_fusion–fission_hybrid