That is obviously a concern and would need to be considered before any plans for the future development of the site were made. Jan and Ian have always made it clear that they would prefer the site to remain as independent as possible and free from marketing.
However, the reality is that as the site continues to grow, the costs of running and managing it also grow. The site is vastly different (ie larger) now to what it was 7+ years ago when we first moved to this current format.
That is a challenge we will need to face at some point, and I know that Jan and Ian are well aware of the issues. I can assure you that Jan and Ian's intention is not to see the site "mass spammed with advertising and marketing" as you put it, nor will it become a closed paid subscription site. Jan and Ian value the community for what it is and are very keen to maintain that value for the benefit of the community.
There may be other commercial aspects of the site developed in the future to help offset the operational costs, but it is more likely to be supplementary to the operation of the community rather than a move to change how the community itself works. The community is the key to the success of this site - it would be silly to change what works so well.