i think the biggest aspect here is the inter-server economy connections
in fact i think the whole thing should be that: purely inter-server economy and communications. i feel the real problem with CityRPG servers is that it tries to contain the whole thing into one server, prompting players to have to invest time on something they may suddenly see disappear the next week.
after reading this i'm getting a new idea; if you want me to remove it just ask, since its only partially related to this mod.
instead of having cities contained on servers, how about a mod that you open up in your own server, in which you build your business/shop and home.
when the server starts and the player's home and business is registered to the main server, the player can choose a business, such as a grocery store or a plumbing business, each which has its own base salary and additional salary. base salary would be given every time someone logs on, once per day, while additional salary is the money they earn through running their business.
then the player gets set-sized lots (width, length, and height) on their server, which are set and cannot be changed. Then they begin building their homes on their server.
economies would be managed by selling their service/products to other players/businesses in need, through the main server. each home would require by default a set amount of food/water/electricity usage, based on how large the home lot is and how often the player opens up the mod. same goes for businesses, except that the stuff they need will be based on their sales.
raw materials and money would be sold/stored through the main server, as part of base businesses which cannot be developed by players (ex: farm, bank, mining facility, oil well, etc)
business transactions like buying food would be processed through the main server. if one needs food, they send their money over the main server to the business, and then receive the product if it is in stock. If it is not, then they buy from a main-server-based business which never runs out, but is only open when no player-run businesses don't have the product they need. The player owning the business must "log on" or open the mod in order to receive their payment and make purchases from the raw material suppliers to restock their shelves, as well as adjust prices. prices would be kept within limits, but very open ones to allow for pricing competition (say, for a raw steak, the limit would be $0.01 to $300).
in order to make such competition less linear and predictable, players can choose to sell price-per-item, or price-per-# of items and then price-per-item after the number is exceeded. For example, someone could sell steak for $16 apiece, or sell $26 for two and then $19 for every one after that.
some businesses, like plumbing, would work through having the customer coordinating a time with the plumber to receive the plumbing, which would simply be the plumber joining the customer's server, or contact through the RTB IRC if the customer can't host a working internet server. the customer would pay a set price (set by master server) to the plumber, and the rest of the bill for the plumber would be provided by the master server. services like these would be higher-paying than other businesses which are passive and checked once-a-day (like selling groceries), but more difficult to get a payday. Their base salary, however, would be correspondingly larger, enough to cover their base utility fees.
if players don't buy the utilities they need after a set amount of time after receiving the (IRL) weekly bill, access to their home is cut off and they need to pay for it if they want to reaccess it.
after a set number of times of opening the mod, players can choose to send their .bls files to the main server where it would be automatically put into a "city" build coded together. this may be too advanced, though, for a gui/server-confined project like this.
although players could probably modify the code and cheat, you, the master server owner, would be able to "ban" cheaters from the master server list, forcing them to start anew.
just some (alright, a lot of) ideas. i know its radically different than what you intend this mod to be but i think this would be a better version of any kind of cityRPG.