There is actually a huge problem here. Most of you seem to assume two things:
1. In site search engines will not improve
2. The quantity of storage shed (in this particular case) images will not rise significantly

First, there is a huge space for improvement for all the sites in case of search engines. In that case the sites will be able to cluster the images better around the particular keywords without you needing to remove those that are not directly relevant to your image.

Second, if the number of images with a particular subject increases to a level, only those extra keywords that were now removed would be the ones that could distinguish a picture from another one. We are already facing this problem in several areas (e.g. images with people or everyday objects on them). Without adding those extra words you will not allow your possible buyers a chance to filter your image from the crowd (e.g. you have a shed with a lamp next to it while the others are not having one and the particular buyer would like to have one in the photo).

If we make the assumptions above then we will end up with indistinguishable images in the near future and it is going to be really hard to stand out from the crowd even in case of highly niche images.

I don't think I should say anything about the commission cut, since it is so well discussed. However, it is interesting to see a change in canister levels similar to that of Fotolia. This new level system is more friendly to new contributors, but still far from supporting new talents. I think the agencies who set up static levels for canisters (like previous istock, fotolia and shutterstock) are still back in 2005 when these limits seemed hard to achieve. Now several contributors reached the limits just because they are participating in MS from early on. It's not that they are so talented, its just that they have started earlier. Fotolia have already realized that the canister levels are not useful without constantly rising the bar, so only those who are talented will stay on the higher canister levels they deserve. However they have implemented this very badly because they set up the levels so high that new talents might not even start after seeing the levels set up for the ones who were with fotolia in the past five years. Istock has made a step further, and dropped the original canister system to a more democratic one, which also supports new talents on some levels. My only problem with their system that they still require you to wait a year to increase your canister level. An ideal system would use the past year as the basis for the canister level instead of using the year boundaries. I would be happy to see this level system to appear on other sites.