Separation of script and display code is important for the reasons you stated. This idea would never replace ATS because the functions in the ATS cover a very broad area. I like ATS, it works very well in most cases, and at the moment it is all that is available for OpenACS.
My motivation for working on this are stated above, where I listed the goals.
In addition, ATS only works with files, making it difficult to apply the separation concept outside of page display. It would be nice to have a merge feature where data can be setup inside a procedure and and a template could be sourced to produce a result. Any place that tcl code is used to create html or text or similar output, this idea would work well to simplify the code.
Also, ATS uses the adpparse code from AOLserver. The tags are actually registered just like regular ADP tags. Because of the design, you cannot rely on the system to protect you from malicious or mistaken programming errors by the template designer. The entire server api is available for their use. This precludes a number of possibilities that I am interested in.
