The issue is that I can't vend a website as a product for reasons I won't go into here -- but I can of course change my strategy so that more of the system is on my own rather than customer machines. At that point I can sanction a browser interface to the system but there will still be an interface to customer-proprietary data (such as configuration files, crontabs and system data they don't want to be stored outside their organisation...) that need to be managed from the desktop and I am certainly considering Tk as the GUI for the client/server interface for that.