If the SNCF has changed their policy and now allows bikes in a housse on all TGV trains, I'm pleased to hear it. As I wrote, that was not the policy 5 years ago. Only some TGV trains allowed bikes. The 2 TGV trains I took in 2004 (Paris to Angouleme, and Bayonne to Paris) did not allow bikes, even in a housse. However, since my Bike Friday folds, I folded it up, put it in the nylon bag I brought with me for that purpose, and carried it on. You originally wrote that TGV trains have always accepted bikes within certain size and container restriction. (I presume you weren't referring to folding bikes, but regular bikes.)

Also, anyone reading this should note the size restriction. 90cm x 120cm is not huge, and a lot of people would have a difficult time, I suspect, readily compacting their bike to fit those restrictions. As you wrote, your container was larger than that, but you were allowed to bring it on anyway. I would simply tell others that they shouldn't assume that they'll be so lucky.

I'm curious if they TGV trains you were on allowed passengers to use the large baggage shelves at the end of the cars, or if they were still blocked off?