If anyone is interested, I've started working on a "source generator" that takes AppInventor block diagrams and converts them to C# code.
The motivation behind this is to use AppInventor as a "scripting language" in C# code. It has nothing in particular to do with mobile apps.
Feel free to check it out at GitHub - paviad/appinventor-csharp-generator: A c# source generator that takes an .AIA exported AppInventor file and generates c# code for it
Cheers!