"The current license for Linux requires you give back any changes you make to the open source community, but there's no way anyone can require those assurances and there's no way we'd know," Rex said.

Hergett said that concerns about Linux security and scalability have largely been replaced by concerns that are more "business-based," such as "open source governance" and the "life-cycle management of a complex stack" with 200 or 300 components.

While Larry Tabb, CEO of market watcher TABB Group, is skeptical that investment firms will adopt open source applications widely because they have such a huge stake in their proprietary applications, he says there is no doubt that Linux adoption itself has become mainstream on Wall Street.