I think it is important to remember that CapMetro Rail had ordered their Stadler GTWs twice. Once before DCTA, North Texas COG, and Stadler went through the long effort to get their GTWs alternate compliant with the FRA. Which resulted in the new Alternate Compliance regulations issued by the FRA.
Second after the FRA Alternate compliance was in effect. It's entirely possible the last few GTWs order by CapMetro might be alternate compliant, and can run on CapMetro tracks with the very few freight trains running over it. And I have no idea what modifications they would have to make to the earlier GTWs to make them alternate compliant. Just suggesting that it could be done.
What I am certain is that the Stadler KISS and FLIRT trains built in Salt Lake City at the Stadler plant are FRA compliant, and that zero GTWs running in the USA were built there.

That's why I am suggesting they might be alternate compliant now, especially if they are suggesting they can operate with freight trains on the Red Line at the same time.,