I also believe that this particular subset of proprietary software is in danger because off-the-shelf software tend to be generic and it's more likely that open-source software will perform the same task.

The more generic the open-source software, the more contributors it's likely to have. Over time it will have similar or better quality and more features than its proprietary counterparts.

There are numerous examples of this.

This is why the web standardised on one language.