In my perception, there are two flaws in the game’s system: huge “external” rewards and level-up inflation.
To add systemic value to grind, economy can be reworked in that only player actions produce value, and that value is generally subject to the law of conservation of energy: souls come only from slaying creatures which have charge count and need to be replenished, gold won in PvP gets stolen from the victim’s funds obtained by manually collecting taxes, et cetera.
This would decrease amount of currency obtained, and lead to rectifying of second flaw: inflation, which could be dealt with by replacing exponential cost growth with linear.
The positive effect of that would be to make player feel actually labouring than getting dumped on with huge rewards, which is the selling point of venerable MMO EVE-Online.
I would quit the game the second they implemented this. Players would instantly spend their gold instead of saving it to be stolen so you would get next to no gold for PvP fights.
There is no way this game would survive financially with a player based economy of any kind. There is even less of a chance it would have any players left.
Trading is out of the question as well, because there are only 10-20 cards anybody could actually want.
The golds pretty much there to level your kingdoms and buy chests. Top guys that have done that use it mainly for their guild tasks which help other players immensely. I see no reason why they should change it.
No thanks to this idea.