I am not sure about 2000 in a stadium, but the idea of outdoor in-person oath ceremonies are actually being done in the US, albeit is small scale, but I think with the right tools and resources, the number can be pushed to at least 200 people in a natural park or other spacious area. If the Montreal office does one ceremony a week of 50 people, this means that around 2500 people give their oath in a year. If we assume 25000 people become citizens in QC each year, this will take years and years to clear the backlog for the oath. I think outdoor in-person oath ceremonies can help clear this backlog. Consider it as a concert. At the gate clerks help with the paper work to enter, and then we all swear the oath before a judge (who doesn't need physically to be there). Tentative ideas that can be perfected by IRCC if they are willing to clear the backlog.