Hi Thomas, testpmd has a 12,000 line parser just for taking in strings and converting it to flow rules. This is obviously useful for testing flows, but it also is an interface for any type of flow imaginable since this is where they're tested.
Now imagine you're developing an application that allows the user to specify custom flows in a config. Your only option is to make your own flow string input (json, etc) and convert that to to the flow spec. This is reinventing almost all of what testpmd already does, and it's extremely error-prone. I think it would be very useful to have this as an API call rather than a user constructing each flow by hand so that all these other applications can benefit and not be worries about bugs during conversions.