Thanks.
Mod doesn't actually implement lua language, and is implemented using factorio's lua modding api, where it evaluates combinator code within a restricted subset of factorio's lua environment.
So its lua version is same as factorio's, and that's 5.2.1 atm, as far as I know, and as mentioned in factorio lua api docs.
If factorio devs update built-in lua interpreter to 5.4 in the upcoming expansion, it'd be updated here as well, but it's entirely up to them, I'm afraid.
Wrt how likely it is - dunno really.
Don't think lua update should break many mods, as it only adds new stuff afaik, and almost certainly should be less of a breakage than major game expansion, so I think it's possible, if dev team finds new lua stuff worth the time/effort, or maybe if modders complain about deficiencies of old lua in this api too.
You can probably check forums for such threads or maybe ask there or on official discord.
