Right so Franklin does not aim to support full LaTeX parsing, rather just get inspiration from these handy new commands stuff.
However there is one thing you can do which might be quite close: using pandoc to go from latex to markdown and then plugging the result in Franklin. And you can do all that from Franklin by using small julia programs which call pandoc when relevant. If this could be something you’re interested in, I would suggest opening an issue on GitHub, I’ve been thinking about offering this capacity and have a good idea of how to do it but it should be tested and discussed.
Ps: I think there’s even a _jll file for calling pandoc