So I'm right!
As a former 'backend' programmer, that's what I thought.
The coding (and server burden) for this kind of functionality would be unproportionate with the gains.
In addition to choke Marketo workflows depending on an arbitrary external server that might even be down, there can be nested 'data value changes' workflows in Marketo that need to be considered to make it synchronous.
Rajesh
In addition to choke Marketo workflows depending on an arbitrary external server that might even be down
Except multiple webhooks in a flow do execute synchronously and are directly affected by external server performance. You can tarpit a flow easily by having a webhook sleep for a while.
Another example where synchronous update is required : Tracking the actions of non-leads
-Greg