The fact that the banner was not meant to be seen does not remove the fact that there is a banner in the works and/or under consideration. If anything, it may increase suspicion of plans to shovel ads to Windows users. It also does not eliminate the fact that there is an advertising subsystem baked into Windows that could be a systemic vulnerability in the operating system.
Microsoft’s long history of taking things that could be good and turning them into operational failures (think ZuneHD) could be at play here. It seems that they like to revisit items that someone thought was a good idea, but annoyed users repeatedly. Each time Microsoft has release internally places ads there has been backlash. It is just not something that people want on their PC. The fact that people are being exposed to ads more often on their mobile devices does not change this fact.
We imagine that Microsoft will put out additional comments on the revelation of an ad subsystem in Windows (not just Windows 11) in the near future with a non-explanatory explanation of its use and reasoning behind it. That statement is likely to ignored and Microsoft will slide again in terms of general opinion repeating the cycle again. We often imagine that Microsoft has a workflow that delineates multiple positive steps towards actual improvement and then a blanket “insert foolish marketing driven idea here” after a randomly determined number of good items. Of course, that could be just us.