Sounds like fun ideas! And in fact not extreeemely hard to program- I think. Treasure Hunt gives the game a little luckfactor, and the Banks add another long term strategy element.
In the very first beta of EC there was a miscommunication between me and the prgrammer. The programmer thought that there where two 'production squares'. A player must own one of these production squares in order to build (aside from other productionrules). It wasnt really playable the way it was programmed, as black would allmost certainly lose the production square.
The idea was pretty fun. You really dont want to lose your productionsquare. So if that happens it's allmost like you're checkmated and you got to free the 'king' (the production square) to have a chance to win.
When I joined this group I was thinking a bit on the rules of economy chess and if things could be changed in order to make things interesting. I ended up with 2 ideas of Economy Chess variants that might be fun to be able to trigger on or off before starting the game. I call those variants "Treasure Hunt" and "banks". Here's how I thought they could work.
Treasure Hunt
In the treasure hunt variant there will sometimes appear a treasure chest on a random unoccupied square. The first player who lands a piece on that square will get some cash and the chest will then disappear. Some more specifics:
The appearances of treasure chests will happen every 5th move. Or to be more precise after whites 5th move, blacks 10th move, whites 15th move, blacks 20th move etc.
The square will not be completely random. If there still is squares on the board that neither player controls it will be a random square among those squares only. If no such squares exist then it will be random among all squares unoccupied by pieces.
The amount of cash there is in a chest will increase for each chest that appears. The first will have 5, the second 10, the third 15, the fourth 20 and so on.
For those that likes configurable options you could be able to change how often the the treasure chests appear (5 default) and how much the first treasure chest will be worth (5 default). Note that this standard setting will make a chest worth the same as the number of moves played when the chest appear. Another option would be to be able to manually put the treasure on the board instead of making it random, but this option is only recommended to use for one player when 2 players are playing through chat in order to put the treasure chest on the same square.
Banks
In the banks variant you will be able to buy banks at the same time you purchase pieces. You can put the bank on any square you control and will be given three extra income for each bank. Be careful though, because if any piece lands on the same square as the bank (regardless of color) the bank will disappear. The bank won't make any difference regarding piece movement on the board (pieces can walk over it).
I was thinking the banks should be relatively cheap and cost about 20. This means you would need 7 turns in order for your bank to make profit. Configurable options are how much income you get in each bank and how much the bank cost.
Of course the final balancing should be based on experience and I'm just guessing with some numbers I think makes sense. I had to chose some numbers to illustrate the idea. Also these variants will not appear in Economy Chess 2.0