Don't see this going much of anywhere, you can't get much more 'Public domain' than what he is...of course he could try to get Congress to actually change copyright and trademark law to suit his taste. Can't use just an executive order to actually change the law, though.
Ironically, this is the most Hitlerian thing he's floated yet, because IIRC royalties on Der Fuehrer's image as used on stamps, portraits, coins, and every other damned thing in Germany from 1933-45 were a constant and lucrative source of cash for Hitler and the Party.