I think Baron gave a pretty good explanation of what stadium theatre is, it's been around for some time, just another medium of entertainment (which can often be coupled with public events production).
Tokyo of course won't consult *with the Chinese* for the sake of it, however it would be logical for a production of this scale to tap into the international major events production family. There are very few people internationally who have the expertise in the production of these events, Tokyo would struggle to go it alone.
The production of ceremonies can go off in a few different directions. Usually, either the OCOG will appoint an artistic director/local creative team (of late these have been film makers, stage directors etc) and then appoint a production company to bring those ideas to life. They will provide the expertise on how to translate those to the field of play (and yes of late this will include how it translates to television - even more so recently where ceremonies have become a set of tableau images rather than a gigantic movement of people and props on the stadium floor). A few examples....
Barcelona 92: Pepo Sol (with support from Spectak - Ric Birch). Also commissioned a number of Catalan theatre companies to produce segments.
Athens 2004: Dimitris Papaioannou (produced by Jack Morton Worldwide)
Beijing 2008: Zhang Yimou (locally produced, granted the Chinese have a lot of experience with their own National Games ceremonies with assistance from international producers)
London 2012: Danny Boyle (produced by 5 currents via a specially set up ceremonies company)
Sochi 2014: Konstantin Ernst (produced by 5 currents)
Alternatively, a production company may bid for the entire ceremonies which also includes the creative side, often they will then bring in locals to help with the creative side. These kinds of ceremonies will often include the travelling roadshow of ideas before committing to a script.
Baku 2015: Dimitris Papaioannou (produced by 5 currents)
Vancouver 2010 / Doha 2006: David Atkins Enterprises
Auckland 1990: Logan Brewer Design
Brisbane 82: Spectak
Sydney 2000: Spectak
Manchester 2002, Melbourne 2006, Glasgow 2014, Gold Coast 2018: Jack Morton Worldwide with David Zolkwer as lead artistic director. (seems JMW and The Com Games have a thing happening)
Atlanta 96: Don Mischer Productions (also worked on Salt Lake 2002)
I think Tokyo will go for the first model, purely on the basis that I haven't seen that many Japanese names being involved in ceremonies worldwide.