So there is. I was looking on Google maps which doesn't show the crossovers but on satellite view (and OSM) they are.There are crossovers between the end of the proposed Newport West site and Ebbw Junction from the relief to the mains, so just run the Ebbws on the newly improved relief lines.
In that case it's intriguing they don't mention this. Stopping them at Newport West at least would make sense to me. Save you having to go all the way to Cardiff to come all the way back again (I know there's an hourly to Newport Central from December too).
I guess maybe they will and they just don't mention it in the consultation as it won't effect all the stations or improve union connectivity.