Google and other engines are starting to use new markups for recipes, and many blogs would need to be converted. Even going forward, the current plugins require their own format and do things like duplicating the post title (not good). If the core code of wordpress' editor included the hrecipe tags it would just solve the problem easily. Same way as we can make a title h1 or h2, just add markups for recipes in the editor and we're done. Super simple, works for millions for recipe blogs.
Converter would also be nice, but more complex.