I think part of the issue is people are assuming these are like domains in 3.5, but I actually think they are meant to be seen as much broader. So Magic is the Knowledge Domain (or possibly Trickery).
I suspect we will know more when we see the list of Gods in the PHB appendices.
Agreed, from reading the fluff of the domains they're meant to be much broader because there are alot fewer of them.
For example in the Tempest domain discription it meantions Gods of Strength, Gods of War, Gods of Courage, Gods of Fire amd Gods Earthquakes, along with Storm and Water Gods. And I think Gods of Air are likely as well. I think that they plan to have all the Elemental Gods like Kossuth to have Tempest for Example, even though its not a great fit.
Trickery looks like it ate the Charm Domain as well, its a Good Domain for Gods of Trickery, Luck, Thieves, Illusions, Charm,Chaos, and Lust. Natures another expansive one, Light Meantions Gods of Light, Fire, and Beauty.
Knowledge could also double for the Arcane, but barely, Light seems better with more iconic wizard spells.
Life is a universal domain to some degree amoung none evil gods.