Yes, the chair was in the conference/ signing room but it's likely an asset that was reused for other scenes. But those lights/ BG are definitely from the Versus trailers/ concept art.
Edit: It's likely that this could have been key art from 2014 before they overhauled the script and design.
Also about Verum Rex: It could very well be just an easter egg. Yet, why it sticks out is because it's an easter egg of something that didn't get to see the light of day. It's also labeled "True King", which is kind of a reading between the lines moment when a project that was just completed constantly used "Chosen King" as it's tag line. Finally, It's a full CG high quality scene that is thrown into KH that just gives a back story to an aspect of the "Toy Box" world. We haven't really ever seen this done in any of the KH worlds before.
That "leak" is really coincidental, if anything. The Nyx thing is kind of redundant, it would be expected if Versus was to happen Noct would be at the invasion like originally shown. If Nomura is planning on rereleasing FFXV as VersusXV, with his original vision, I'd be down to play it. It would be interesting to see how much the characters will differentiate (this is kind of the same realm as what Type series was going to do) and the combat will be likely be better, based on how it was supposed to be closer to KH battle system. That being said how funny would have been if this was Luminous 1st project they had to worked on and because Tabata had openly stated he didn't want to work on FFs (or atleast a main line) again this is the reason why he left.
Edit: It's likely that this could have been key art from 2014 before they overhauled the script and design.
Also about Verum Rex: It could very well be just an easter egg. Yet, why it sticks out is because it's an easter egg of something that didn't get to see the light of day. It's also labeled "True King", which is kind of a reading between the lines moment when a project that was just completed constantly used "Chosen King" as it's tag line. Finally, It's a full CG high quality scene that is thrown into KH that just gives a back story to an aspect of the "Toy Box" world. We haven't really ever seen this done in any of the KH worlds before.
That "leak" is really coincidental, if anything. The Nyx thing is kind of redundant, it would be expected if Versus was to happen Noct would be at the invasion like originally shown. If Nomura is planning on rereleasing FFXV as VersusXV, with his original vision, I'd be down to play it. It would be interesting to see how much the characters will differentiate (this is kind of the same realm as what Type series was going to do) and the combat will be likely be better, based on how it was supposed to be closer to KH battle system. That being said how funny would have been if this was Luminous 1st project they had to worked on and because Tabata had openly stated he didn't want to work on FFs (or atleast a main line) again this is the reason why he left.
Time for me to come back about the whole Nyx things. The guy posting the rumor said The Nyx thing could easily be scrapped so Episode Nyx or maybe they were thinking about a Kingsglaive game because I remember at GDC Tabata was talking about how Ardyn couldn't fit into a DLC Episode so they decided ok we'll make a game about it maybe they thought of doing something with Nyx and Insomnia for sometime but couldn't pin down what they wanted to do with it and ultimately scrapped it. I'm also thinking that the reason why it was mentioned was if you look at the picture of the rumor the title of it is 2020.png so let's say a Kingsglaive Nyx thing whether that's Episode Nyx or a Kingsglavie game were to have happened it would be due to the fact Nomura was busy on KH3 at the time so they maybe to speed up development of a supposed Versus XV they made something with Insomnia for Versus XV to reuse later.
Also Verum Rex I heard is an actual world that Sora can enter and play the Verum Rex mini game it's not a world like Traverse Town I think it's more comparable to Keyblade Graveyard in KH2FM where it's a world in the game but not explorable.
So Verum Rex goes beyond simply an easter egg and is a playable mini-game within KH3 it's even on the trophy list. I mean if that's what this rumor meant by a XV/Versus world in KH3 I can somewhat believe it it's not like the FF characters in KH are 100% true to their original counterparts and maybe Verum Rex was originally more XV/Versus XIII but they didn't want to make it too obvious but obvious enough for you to see it.