I think they were planned to be capitalists from the first. They came out of the writers wanting a scary alien race to replace the Klingons. It shows how extremist the writers room had become that what they came up with was capitalists. They only scrapped the idea of the Ferengi becoming the new antagonists after screen tests gave them a reality check.
Their second attempt at this created the Borg though, so they did get it very right in the end!
Their second attempt at this created the Borg though, so they did get it very right in the end!