This would be good so we don't have to download the file, edit it, and upload it again.
eyebex
in case you mean by "html editor" a full-fledged wysiwyg editor, or even just a good html code editor: that would be way too complex and would easily double smartftp's code.
in case you mean a feature to edit a file "in-place" on the server (which just means that up- and downloading are automatically done in the background) with any editor installed on your system: this has already been discussed, see the links below (just the first few hits from the search).