I booked a ticket on the brand new direct Berlin-Paris day train connection and the overall experience was extremely satisfactory:
* easy to find on sncf connect
* easy to combine with the Paris-Le Mans connection
* actually cheap!
* could book now for early January (not for later in January though)
Very different experience than the ones I had trying to book the night train (in which I have managed to book for the first time for early December, for a very decent price).