The linear functions/SMC work is really cool, but I am surprised to see the author calling it more mature than the compiling to CCCs work. The linear-smc library hasn't had an upload in a while, and it's currently missing any haddocks beyond the extracted type signatures. It's also a shame that it had to build its own typeclass for monoidal categories instead of using the one in https://hackage.haskell.org/package/categories .

Meanwhile KittyHawk did actually use the compile-to-CCCs work to compile Haskell to C in https://github.com/sellout/compiling-anything-to-categories and someone from there talks about it at https://www.youtube.com/watch?v=VUBj8NW7uMA

I think the linear-smc work is more exciting and I hope it matures with a bit more elbow grease. There was an ICFP talk that accompanied the linked paper ( https://www.youtube.com/watch?v=90OJz0QE4qE ) and monoidal categories can model lots of "boxes and wires" things. Linear functions potentially give you a much more ergonomic DSL for building up those boxes-and-wires models, and in a way that lets you write abstractions that work over any model.