I don’t believe that we should rule out the possibility of having the future Mathematics Student Journal (MSJ) under the sponsorship of only one giant corporation. The Science Talent Search (STS) thrived under the umbrella provided by Westinghouse Electric Corporation for 57 years and it continued to do well as the Intel Science Talent Search from 1998 through 2016. Presently, with Regeneron Pharmaceuticals as the new sponsor and with Covid causing lots of disruptions, the success of the STS is in doubt, but its continuity is assured.
While I don’t know how Regeneron surfaced as the new sponsor, I remember that Intel had to outbid several companies to get the STS in in 1998. I doubt that the Society of Science had better arguments for starting the STS in 1942 than the former Contestants of the Competition Corner have now, in 2019 for launching the MSJ and yet they managed to win the Westinghouse Electric Corporation to their cause.