Hmm. With as vast as Usagi's kingdom is I assume a lot of country/planetary pride would remain. People on Mercury are so much superior to people who live on Mars and so on. Not to mention the xenophobia that will probably appear when people start leaving their planets for assorted reasons to join Neo-Queen Serenity's kingdom.
There would also be the lack of support for Chibi-Usa, even though she left to the past to train. The people would probably still see her as that six year old that stayed that way for 900 years until she ascends like her mom and grandma into
Princess Lady Serenity
I can see allied planets like Kinmoku, and Mau doing exchange programs so their people can see how the other lives, their technologies, their abilities and their culture. I mean Makaiju were born from trees and Mau/Coronis/Cocoon can turn into animals.
I think a place like the Galaxy Cauldron would remain untouchable ground and be kept secret from any-non senshi. It would be too easy to have a repeat of Galaxia. The Space-Time Door, still closed after sealing Pharaoh 90 would be forbidden for similar reasons,
The keys to Elysian being opened would probably lead to amazing finds. Since it's all that remains of the original Golden Kingdom and earth before it's evolution was restarted.
Setsuna, alone could probably answer any answer lost to time.
With Open planetary borders I can see creatures that aren't Chaos related like the
Xenian flower flourishing across the galaxy. It could do a lot of damage if it finds a host.