It would be very nice to make all the settings
changeable (maybe only before starting the server), for
example:
-changing the number and sort of cards in the game
-rule dices AFTER building roads (or building, dicing,
building)
-quota's for building roads/settlements/citys/ships
-if a robber is used at all
-which components and add-ons are used (city's, but no
ships, for example)
-whether resource- or other cards are visible for all
players (available for each card type for its own)
Also the "Cities and Knights of Catan" Add-on would be
nice.
Start with making all existing game rules editable, would be very nice. Makes a lot of sense when you want to play a certain map with a different number of players than normal. Then consider adding new non-standard options like rolling dice after building.