For example, I'd like to remove the N first characters of each line, but the first and last lines contain less than N characters.
Emacs: start selection at the first line and simply add the missing number of characters (e.g. spaces) to the last line and then use kill-rectangle
Alternatively, see artist-mode or picture-mode which allow you to freely move in the window regardless of line lengths.
Paste block inline
Emacs: First save the block by either kill-rectangle or saving it to a register, then go to the insertion point, use delete-rectangle and then insert the saved rectangle.
looks like a 400+ lines plugin is necessary
In case of Emacs why is it a problem? A plugin can be compiled and the emacs philosophy is you don't put everything into the core, but use plugins to extend the editor.