I would like to add excerpt from the news link about NASA'S VIPER robot and Open Source Software (OSS):

VIPER isn’t running on 100% open-source software—its onboard flight system, for instance, uses extremely reliable proprietary software. But it’s easy to see future missions adopting and expanding on what VIPER will run.

It will never be possible to use open-source software in all cases. Security concerns could be an issue, and might cause some parties to stick to proprietary tech entirely (although one plus to open-source platforms is that developers are often very public about finding flaws and proposing patches). Some missions will always be too specialized or advanced to rely heavily on open-source technology.