Now that the extended deadline for submissions has come and gone, the Senators (as part of Rendez Vous Lebreton) have made it to the next round of the decision making. The other group that submitted a proposal was DCDLS Group (formerly Devcore). The only detail we know of their proposal was that it was to include a "grande allée" with multiple cultural institutions.
Neither Focus Equities (international organization HQ) or Claridge Homes (concert space) submitted a detailed proposal.
The NCC will take the time between now and the public consultations on January 26th and 27th to go over the proposals to ensure they meet the requirements.