I was staying in Offenbach last time is was there. Took the S8 into the city everyday; one point you're going through the neighborhood above ground, then all of a sudden you're underground and in the heart of the city. Really cool experience! ICE has plenty of services to Frankfurt Hbf too, just a thought!
It would actually be to longy that DTG would all it, but they can do parts of the route for example we already have Cologne to Aachen, so they can add the Köln Rhein Main route and the route from Aachen to Brussels
Which is bascially a route extension for a route that everybody owns and would intrest people who are intrested in high speed german routes and can be standalone routes as well. It seems a no brainer for them to do