Currently, there is an issue with custom K events, such as "K:A32NX.CustomEvent", where they cannot be used in XML RPN, even though they are being registered in a WASM gauge via SimConnect. Trying to do so results in an error in the console:
This severly limits their usefulness, and although they can be triggered in JS via SetSimVarValue, creating a sort of "relay" via JS and H events is very tedious and makes everything more complex than it needs to be.