As I recall, there were a number of games that had a modest amount of commercial success that were made with the GCS, which was, essentially, a first person shooter creator. That's also been true of a few of the non-fps-creator tools.
I think it's the innovation, creativity, and skill of the creator that's most important, not the tool. I agree that FPSC is more limited than many of the negines out there (like DBPro), but I expect that many people will be able to make some money off FPSC.
There are also those, like fdecker, who won't make money by selling games directly, but by using FPSC to educate others. I can envision a number of educational uses for the product. I can also see it being used for advergaming, product demonstrations, live walkthroughs of proposed buildings or homes, etc.
Basically dark.