Some nice ideas in there.

Only the "markdownquote" thing is kinda pointless, especially since they mention it's mainly used in vim. Because vim can do exactly that already without the need of an external script. Do ctrl+v, mark the lines you want, press "I" (capital i), insert the desired thing, press esc and voila... all the selected lines are now prepended with the desired thing.

edited to make my comment sound less harsh: Nothing wrong with building your own solution if that feels better to oneself though :-)