Well, the project does mention that they're not trying to replace any existing approach but instead provide additional functionality over the existing stuff. My understanding is that they can grab the JSON, XML or whatever else other projects do, use some existing tool on the parsed data and then passing it forward to other tools as JSON, XML or whatever. I think the diagram at the end of [0] shows it well.

[0] https://relational-pipes.globalcode.info/v_0/index.xhtml