When ppl take about an expansion its like new boards ect , I personally think this game would benifit from an expansion in the future but defenitely not a new board. My idea is add to what we already have meaning new versions of the gods (new dial advancement , draw phase , even minions) , new cards for each god , new old world cards , and you can always add a little without changing what already works.
One idea I have is a "new" game mechanic - 1 per game abilities. Lets be honest we "play" as gods but it doesnt seem like they really get involved in the game too much , sure they have thier ways of winning but no real impact themselves.
E.G. Khorne-Once per game for each area that you have a minion in you may destroy a minion to destroy an opponents minion of the same type (cultist destroys cultist , ect) this does not advance you victory dial.
E.G Nurgle-Once per game goto each area and add up your corruption there , for every 2 corruption you have there you may gain 1 corruption this does not advance your victory dial. If this would cause the area to become ruined you may choos to ruin that area immediately or wait to check for ruination.
E.G Tzeentch-Once per game for each area that there is at least 1 warpstone you may place 1 warpstone in that area or move a warpstone to an adjacent area , this cannot cause more than 2 warpstone to be in each area.
E.G Slaanesh-Once per game for each area that contains 1 or more peasants you may chane 1 peasant to either a noble or a hero , or move 1 noble or hero to an adjacent area.
One other idea is your upgrades , I have an idea for "high risk" upgrades meaning better reward but higher risk to play.
E.G Nurgles cultists-Your cultists provide you with 2 corruption each but you maynot have more than 2 cultists in any one area , costs for you to play them would be increased to 2.
That the only example I have off the top of my head for those so far.
Then Old World cards.
Cleansing the World - Roll a die , whatever the number that appears place an event marker in the region worth that many victory points (most corruption breaks ties) do this 3 times total , at he end of the battle phase all corruption is removed from any area containing an event marker. A rolled 6 means no marker.
I am thinking of some other cards and such but these are just my thoughts. Thanks for any feedback.