I am new to MT so I don't know if this exists already:

It would be nice if there were a way for a blog owner to be able to create and define multiple entry fields of various sorts (text boxes, radio buttons etc) which are placed in the entry itself, where the visitors can input data. The user-inputted data is the stored in the sql database and can be subsequently used as blog owner sees fit by defining placeholders for each of the fields.

right now, the only such field is the comment field, and perhaps the comment title field if you use the plugin -- but I would want to define as many other fields as I want, each of various sorts, which the visitor/user can use to input data. Also, ideally, I would like to have a way to perform basic manipulations of the user inputted data.

For example, on the simplest level, how about a 'rate this entry' field which is defined as consisting of numerical scores between 1-5, which the user can select from a drop down menu. There should be a placeholder {$MTintegers$} that will spit out each of the scores selected by visitors, and another placeholder {$MTNumericalAverage$} that will spit out the average of the inputted scores.

The custom fields plug allows the blog owner to define custom fields for his own use, not the visitor/user's use, as Iunderstand it.

This would allow for a much greater interactivity.