I enjoy your show, so it's a little disconcerting when you take on a subject a little closer to my expertise than usual and I find the presentation misleading. As far as I know, the wormhole solutions to general relativity which your physicist guest blithely discussed cannot be made stable unless a form of matter known as 'exotic' with negative mass is found which can be used to stabilize them.
Such matter is not currently known to exist. Therefore I would not regard use of wormholes for time travel as merely a matter of technical development, as your guest seemed to imply.