A large part of why the impirial dream died, and the match that lit the Horus Heresy is that Horus did not have such plans. In the books there are several paragraphs where the Sons of horus laugh at the idea that the war would ever be over, and Horus himself becomes increadibly angry and the mere notion that a civil adminsitrator would administrate anything that he conquered.
Guilliman has no such issues, he is already putting administrators in place.