For me, this is a disappointing article. I agree with you that regular expressions are not used every day and for that reason can be difficult to master. But you highlight examples of trivial expressions because these are easy to present in a visual way. What about conditional look-aheads, named capture groups or other elements of an expression we should be using but for the syntax is even more abstruse?

Also, you do not give credit where it’s due. There are sites that have attempted to do an admirable job. https://regex101.com/ attempts to provide an English-like explanation of the components of an expression. http://regexr.com/ highlights logical components of an expression with popups explaining the components as the mouse hovers over. https://www.debuggex.com/ even already provides a visualization of an expression that changes as you type, much like you suggest except the visualization itself is not editable.

Each of these examples appear on page one of a Google query for a ‘regular expression editor online’. Unless you are responsible for one of these, especially Debuggex, to me your article appears derivative.

And to backup the comment made by at least one other, these sites also attempt to support the differences between the implementations of regular expressions engines different languages.