It’s a good start, though they’ll need more than one train a day. This isn’t Australia.
This is just an additional direct train. There are several such connections with a switch in Cologne or so daily.
And there's also the Munich-Paris line in the South
Tickets are on sale now, starting at €59 one way.
That is really cheap.
For anyone else that's curious about a comparison in the US, I looked up Amtrak from Atlanta to Washington DC, roughly the same length. $109 ticket and it lists just over 14 hours to travel. Based on what I've read it's practically guaranteed to take a good bit longer though.
So ~75% higher cost and at best ~75% longer travel time.
"Starting at" means if you book 3 months in advance and are lucky to get one of the rare discounted tickets. Normal price is probably the triple of that or so.
I picked the cheapest ticket for the US trip. It's as fair a comparison I'm going to get without checking the trip to Berlin. Which I don't want to do, if it's even possible yet.
Everything about public transportation!