I started developing uniGUI (or whatever name it may adopt in future) around two years ago. Since then it has evolved a lot. Initial version was based on VCL for the Web. With addition of ExtPascal and Ext JS it has become a very advanced tool to develop Web apps based on Delphi.
uniGUI simply defines itself as a Web Application Development framework. The concept of Web Application has been controversial since its first inception. Some people claim that Web is stateless but applications are statefull, one should not mix these two. However, nowadays with an increasing demand for web applications such notions only remain as a philosophical point of view.
More and more people want to access their desktop apps from the internet. Companies want their local accounting software to be accessible to other branches. A security company wants a web gateway for their access control software. These are all examples for the increasing demand for web apps.
We can consider uniGUI as an abstraction layer for Delphi VCL controls which extends them to the Web. Like all other abstraction layers it helps developer to focus on application logic rather than the development tool itself. It tries to fully integrate the RAD approach into Delphi based Web development.
Dual nature of uniGUI is simply a plus. I'm referring to its ability to deploy same application to both web and desktop using same codebase. This feature maybe useful for some developers but useless for others and it can be completely ignored by those who focus on Web development only.
As for the scalability, the best target for uniGUI and other similar tools seems to be the intranet where the number of clients are predictable and connection speed is a non-issue.
That said, nothing prevents developers from developing web apps that target the internet. At end it is all Ext JS on the client side and Delphi event handlers on the server side. It all depends on how smart you design your app and how efficient you manage your resources. If each of your sessions consumes 10 MB of memory then you're likely to run out of memory very soon.
In conclusion, this framework will have a group of users which will find it best for their needs. There is no black or white here only big gray areas. Like any other tool it depends on the company, the particular project and the available deployment options to see if it is the right tool for you or not.