I've taken trips on the TGV, the Eurostar, the American Orient Express and, many years ago, even on the New York Central's 20th Century Limited. While I consider riding first class on any and all of these trains to definitely be "luxury" travel, I have NOT taken the TGV and Eurostar trains on overnight trips. So, at the end of the day (no pun intended) I guess that, if I'm going to be sleeping on the train and if I don't have a compartment with its own bathroom, I wouldn't consider that a luxurious experience.

I agree. Though, I may be wrong, but I don't think that Eurostar or TGV or any highspeed trains have any sleeper cars. It's not that often that you're on a high speed train for 7 or more hours.

So, I think it would depend on how long the trip is. If you are doing an overnight sleeper, a private bathroom and sink is a must.

I've done a number of overnight First Class sleepers in Europe. Every First Class overnight compartment that I've been in had a private bathroom. Some even had a shower where the entire bathroom was the shower! For me, it's not a question of luxury. Private bathroom are a necessity for overnight trips.

But, for daytime trips, you usually don't need a shave and a shower, so the private bathroom is not as important.