Fernando Melo, just saw a new item (MC165551) in the message center about some of these features. Looks like those features will be there by the end of December worldwide.
We are updating the “change the look” settings with additional options to enable customization of select site brand elements – specifically, header layouts, footer layouts, and navigation menu options. In addition to setting the theme and header background, site owners will now be able to switch the site header layout to two other layouts, each changing the position or displaying of header elements. The new mega menu navigation layout is only available for horizontally-oriented navigations and allows for a panel display of links up to three levels. The footer setting is initially only available for communication sites, displaying a footer that can host a logo, links, and label.
We'll begin rolling this out to Targeted Release organizations at the end of November, and the roll out will be completed worldwide by the end of December.
Source: https://admin.microsoft.com/AdminPortal/home?switchtomodern=true#/MessageCenter?id=MC165552