It is always interesting how disagreements remain hidden until you actually start making things concrete

1) The "engine" is responsible to turning universe+orders into a new universe.
2) Some other program (e.g. the current starserver stub) is responsible to handling the external interface, validating and merging files, keeping track of state, etc etc.
3) The engine consists of approximately* one module for each item in the order of events

4) Each module takes universe+orders as input and outputs the new universe (optionally plus the orders)

python-pseudocode for the engine (taking http://www.starsfaq.com/order_events.htm as reference)

def process_turn(universe, orders):
universe = scrapping_fleets(universe, orders)
universe = manual_load(universe, orders)
universe = wp0_unload(universe, orders)
....
universe = remote_terraform(universe, orders)
return universe

1) How is state encoded and passed between modules? My vote (at least for the time being) is json, since it is flexible and easy to make changes to. XML is imho too cumbersome to parse and manipulate, plain text is too fragile.

2) How are modules called/coded. I would still really argue against writing modules in different languages* and using system calls, but of course that is possible.

However, I would think that the logic in most modules is not actually that difficult, and porting existing e.g. C++ modules to python (or python to C) should be not too much work compared to making sure that existing modules deal with the state as agreed on in (1), which is necessary anyways.