The totally awesome Community Addons project developed an On Variable Changed unit:
which acts logically as:
to which you said:
But your On Variable Changed event should deeeeeefinitely be built in! Could you post a feature request?
The community implementation is here:
with additionally relevant files at:
Though some of this you will notice is a direct clone of your own source code, which I can't use as it is target at the base class UnifiedVariableNode (which I can't use for the event) as opposed to the interface (which I could use).
Customer support service by UserEcho