Just because reclining is not a part of modern culture doesn't mean the Jews should stop doing this at Passover. He mentioned in the video that poor people didn't have to have special furniture to be able to recline and this was acceptable. If this is true, they were not truly reclining like nobility but it was still acceptable to perform the mitzvah. So therefore people who recline today don't have to do so exactly like Greco-Romans did with the special furniture, as long as they are reclining in a way that is distinguishing this meal from other meals. The Mishneh Torah does not really specify the form of reclining other than the fact that you recline on your left side.
No, I think the translation is wrong. Hasiba isn't "reclining". What most people do today is not Hasiba. Its just leaning to the side and eating backwards. It shows no sign of freedom and nobility and in fact the opposite as it isn't even comfortable.
Very very few people actually do Hasiba.
- The question is why the Rambam says to do it and why many Askenais Rishonim already say not to- that is because of the way people ate at their respective societies. At the time of the Rambam doing Hasiba was a normal way of eating especially for the "higher ups" of society, while in Europe people ate in chairs and such. That is why the Hachamim commenting on this said to eat in chairs and not to do Hasiba.
This is a Rabbinic decree (maybe even less, maybe can call it a custom) with a reason given- to show freedom and act like royalty. That being said leaning or tilting to the left side (as is commonly done today) isn't any act of nobility, nor does it show that one is free. If anything it is the opposite.
Doing Hasiba properly, the way it was done beforehand and the way that few (Rambamists) do is still not necessary as this is not a way to get across the message of nobility and freedom and such today.
Today we can and should sit in nice, comfortable chairs that we have. Perhaps include a pillow and get more comfortable. But that's about it.