Right now, there is no information about this event other then "It is happening". No details about what sort of event it is, who exactly is involved, nothing.
The English love liver community has spent the last 26ish hours going crazy over assumptions and speculation that is baseless until we get more information about this event. If/when they announce that the event is not what people are currently making it out to be, there is going to be disappointment all round. Can't people just wait until we have something more then "an event is happening" before they go nuts?
Aqours 5th live is next weekend. They are likely to announce some more info about this then.
Meanwhile, people seem to be ignoring the other big announcement made in the same stream, the 2020 live tour. Which could be a world tour, but again, we don't know because they only said "this thing is happening - all details later".