It is reasonable in a way. Let’s say you want to write an Internet-based application that interacts with sketch up files. Maybe it is just a simple viewer where it loads the sketch up file and displays it in the web browser. Maybe it lets you create geometry in the web browser and then download that as a sketch up file. Both of these are possible using the SDK.
Now if you are running a Web app, chances are likely that the operating system that you use is linux or another UNIX-based system. Having a Linux SDK for sketch up would allow developers to write applications on Linux that work directly with the sketch up files without needing to have a Windows installation and running the graphical front end.