And they don't need anyone's permission to do so. They don't need to comply with any Windows user interface conventions. They don't need to display Microsoft icons or logos. These appliances will almost surely run on Linux but won't be marketed based on the fact that they run on Linux. All it takes is one smart company to see this opportunity and grab it.
Someone is bound to answer the call.
A few companies are already on their way. It'll continue to run the World Wide Web. It'll continue to grow in the middle tier. It will continue to displace Windows departmental servers. And it should displace most Windows desktops with something normal people can use, but don't have to manage.