displays the number of input characters entered in forms or text areas
http://kmext.sourceforge.net/files/charcount.7z
text-input context>character count

update adds an auto-count layer
textpopup>auto count

Could this be implemented for panzpad or panzpad plus extension?

maybe in panzerpad.. i'll look into it but not in panzerpad plus because it's richtext html form and the js won't be able to recognise characters from it, you can use the character count menu which will count any text and doesn't care about form type