There is no news about the trading system of the game.I am a bit unhappy about some stuff choosen from Heroes 3 rather than 4 but this is definiately a place where Heroes 3 shines.
-IMO the trading system should allow to send resources to all players let it be friend or enemy.But ıt should have a delay of turn based on the distance between the nearest castles of players.
-Market place should be again a bit more expensive ı think.It was just easy to trade resources and build a castle.but in heroes 3 that didnt happen so easily if you were going to build a dragon cave you should have a sulphur mine.
Lastly tradind with enemies is essential because it allows bribery.Or you can supply a weak player so that he is strong enough or can cause heavy causalities to the strongest player in the game.Alternatives goes so on and is very essential in keeping the game balance and makes the game more diplomatic.
Also ı hope there is a way of sending artifacts also.