Thanks. A proper writeup would make sense. The README documents the individual parts, but it does not really explain how they fit together or cover the stranger Java ME issues that came up along the way.
The project has three main layers. At the top there is the MIDP interface and cartridge management. Below that is the WASM-4 implementation for graphics, audio, and input. At the bottom is a small WebAssembly interpreter. A writeup could cover memory limits, bytecode preverification, differences between Java ME implementations, and the parts that had to be tested on real devices.
The SIM card idea is more complicated. Programmable SIM cards usually run Java Card rather than CLDC/MIDP. Java Card does not provide the usual display, audio, or input APIs, so W4ME Station could not be ported directly.
A small command-based WebAssembly experiment on Java Card may be possible. A playable WASM-4 runtime would need a separate implementation.