In alternative to what michiecat said, I think this could be doable using the display-posts shortcode. This shortcode serves to list the posts you want to display, in various ways, and, dynamically--automatically "updated", you don't have to worry. In that case, how would it work:
- As you want to flexibly change between articles, I think instead of using the ID to filter, using specific tags would be better, one for each ("featured1", "featured2", "featured3"). That way you won't have to change the shortcode, just assign the tag to a different post instead.
- So you'll have 3 shortcodes, each filtering a different tag, each one displaying a single post (each tag assigned solely to one post at a time).
- As you want the posts' featured images to be displayed and not their title, you'll also have to customize the shortcode in that way.
- Concerning the size of the images, you'll have to customize yet again the shortcode to make their size full. In the case of the half-width images, I think maybe the best approach is to wrap them in 50% width divs (shortcodes inside the div tags).
However, I haven't tried it. What do you reckon about this, michiecat?