Is there any link between this and the recent announcement FS2020 will be supporting the FSX XML gauges in a near future?
Nope, I don’t do FSX conversions. If this helps them in some way though, that’s great!
Is it parsing a RNP file and converts this to XML file, or is it directly translated to XML in memory so that FS2020 is using the translated RNP directly?
The package itself is just RNP to RPN. It is intended to be used in conjunction with a tool which parses and modifies the XML source files. I’m not sure there would be any way to modify the files in memory (And I’m not sure you’d want to do that anyway, since you can do it ahead of time). You can see a (work in progress) example of a script which converts XML files containing RNP here: https://github.com/flybywiresim/a32nx/blob/rnp/src/behavior/build.js
What was the main driver for creating another script language instead of for example using the ubiquitous LUA?
Lua is a great language, but it can’t be (trivially) compiled to RPN. The runtime object model would likely require more than the 50 heap slots that RPN provides.
And actually while at it, instead of supporting XML natively in FS2020, why not having a XML to JS translator and just code in JS natively?
I’m not sure I understand the question here, but this is generally intended to be used in model behaviors more than instruments.