This is an interesting proposal though I'm not sure it'll come to much. It's an awful lot more complex than any of the commercial GM plants, requiring a number of genes spread across multiple cells all of which need to be switched on at the right time and place, plus structural changes to the plant leaves whose genetic roots apparently aren't understood: https://c4rice.com/the-science/engineering-photosynthesis-wh...
I agree. The researchers are aware of the challenge. There is so much we don't know about the C4 pathway and then to somehow successfully merge parts of it into a C3 plant. It might be easier to develop a C4 plant that can thrive in a rice-centric environment.
