There seems to be some disagreement as to whether or not the Revolutionaries will be attending the Reverie. This is because it seems like they have nothing in particular to gain by attacking the Kings. This would be way too public for them.
However with this meeting taking place, it seems to be the perfect time for anyone to want to take part.
Why?
Because of the sheer amount of information that will be passed during the meeting.
Back-tracking, during Dressrosa, the Revolutionaries did no major fights (apart from Sabo when he saved Luffy). This is because they wanted to keep their plans hidden from the World Government (seeing as CP0 was in town).
Thus, it would make sense for the Revolutionaries to at least send a spy/spies to gather intel. Not only can they gage each country’s leaders worth, they will be privy to details about global issues, in other words, global weaknesses. The World Government’s possible secrets and trials.
So with such a great opportunity to gather intel about their enemies, I ask: would Dragon really give up this chance to gain the upper hand? He could send in just 1 spy. If the spy is successful, he gains so much more than if he loses a spy.
Theory by Ruruya