There is no concrete plan or roadmap for adding LPE support to Cycles currently, but I think it would be useful functionality to have.
In my experience LPEs can be implemented quite efficiently and in a way that works well on the GPU. The state machine can be compiled on the CPU. The kernel just has to track the active state number, and update it following the state machine on every event. Whenever you accumulate light or albedo, you would then loop over an array of active AOVs for the current state.
Parsing of the expression into a state machine can be done with OSL, which can then be converted to a representation that works on the GPU.
If implemented well this can actually simplify the kernel side render pass code a bit, and handle light groups with the same logic.