IMO, the DMG shouldn't be written for newcomer GMs - they're better off being pointed to the Starter Set and the "how to DM" videos that of course WotC have on their various channels. (I mean, surely they must have such things, and they're really easy to find...?)
IMO, the DMG should be aimed at DMs of intermediate skill - they should be assumed to have already run a game or two, know more or less what's what, and therefore the goal should primarily be to provide practical tools and experience to help them make their games better. So provide lots of tools to reliably construct encounters/adventures/campaigns of various types and styles, discussions of player and DM types and motivations, and so on and so forth.
(And the DMG probably shouldn't be aimed primarily at expert DMs either. Partly because they probably know it all anyway, but mostly because such DMs are inevitably very much the minority.)
My hopes for the new version of the game are mostly pinned on this new DMG. Alas, those hopes are fading.