I'm not familiar with the details of that API and how it translates into the engine API endpoint, so others might give better answer here. But I suspect that there are conditions where a variable could change where the selection state is not affected. An obvious case would be if the value of the variable is changed explicitly and not through a change in the app data or selection state. I'm therefore not sure the approach you describe here will be complete and capture all cases where the variable changes, but it all depends on your particular use case! I assume listening on the selection state change events should capture most of the cases, so it might certainly turn out to be sufficient in your case if the conditions are right.
