The Eurostar web site now allows connections and through ticketing to select German cities using the services of DB rather than Thalys.
The cities included are Aachen, Bonn, Cologne, Dusseldorf, Frankfurt and Munich. You change in Brussels.
The fares are not totally competitive to the airlines, but it does allow some flexibility in that you can get any ICE train on to your final destination from Brussels. Some cities require two changes.
With DB not coming to London in its own right for some years, this does open up Europe (a little) for now. Fares are either in Standard or Standard Premier. I assume the connection on DB is in 2nd Class.