Actually, I realized that some site owners may prefer the smaller image size, if only for a faster page-loading time (if the original image is really big, it wouldn’t make sense to load the entire thing by default).

So instead of changing the default maximum resolution of 700px, I will make it possible to override the default and provide any of the WordPress Thumbnail sizes (in your case, you’d probably want to change it to 'full').

Please see this comment on GitHub for an example of the code that will be necessary to override the default. This ability to override the default Full-Width Featured Image size will go out with the next theme update.