It's not a terribly complex modification, but it may be better to think about exactly what information is needed for such a purpose and then set up a custom object which can be queried for using Nettool. Most of the Nettool functions are password protected, so maybe we can leave it up to the server admin as to whether this extended query mechanism requires a password or not (or allow it to rate limit the requests or something like that).
So what fields do you need? Currently the gameinfo object contains:
# 1, xml version, none
# 2, simutrans version, tag params - version, pak
# 3, object name (gameinfo_t), none
# 4, x dimensions of map, i32
# 5, y dimensions of map, i32
# 6 - 4101, minimap data (64x64px), i8
# 4102, no. of industries, i32
# 4103, no. of tourist attractions, i32
# 4104, no. of cities, i32
# 4105, population, i32
# 4106, number of vehicles, i16
# 4107, number of stops, i16
# 4108, total passengers transported, i64
# 4109, total mail transported, i64
# 4110, total goods transported, i64
# 4111, total goods transported, i64
# 4112, freeplay on/off, bool
# 4113, timeline on/off, bool
# 4114, starting money, i64
# 4115, current year/month (how is this field represented?), i32
# 4116, bits per month, i16
# 4117, language code, CDATA
# 4118, game comment, CDATA
# 4119, samegame file name, CDATA
# 4120, pak name, CDATA
# 4121, game engine revision (svn version), i32
# 4122 - 4137, player type in each slot (1-16), i8
# 4138, total number of clients, i8
# 4139 - 4158, checksum??, i8
# 4159, closing object name tag, none
# 4160, blank, none
# 4161, closing simutrans tag, none
