Yeah, in the last livestream they have spoken a lot about amenities, but they were not very clearly about the distribution in case of multiple ressources of the same luxury.
I think I remember they said One luxury -> 4 amenities -> that's it. BUT they just had 3 roman cities plus 1 conquered. So it was unsure if they meant it in general Or for that certain case.
It can be both way atm. But yeah, I agree it would just be weird. But in CiV it was kind of the same, you could have 5 copies of one lux but just support 4 happiness. It was weird but okay, happiness was global counted and only one lux counted there. Sure You had Buildings which provided local happiness, but now the "happiness" is, god thanks, counted local. So I really hope that multiple sources of the Same lux can Support more cities and if you prefere a smaller empire, you can trade your extra copies to get a higher diversity of amenities to support your fewer cities...
Just hope that some youtuber will show us it today or in the next days.