Imagine the joy of first building a cheap, sturdy and beatuful bridge, and then enjoying it as a part of a track in a railroad game :-).
You could make this a co-op game, where one player is responsible for making the bridge, the other for building the track and loading the train etc. Imagine the fury when your bridge collapses, because your buddy sends a too heavy train over your bridge :-)
I know making a train sim is probably a LOT of work, but how about making Pontifex a module for example the 'trainz' train simulator game?
For more info about 'trains' follow this link:
http://www.auran.com/trainz/overview.htm
This train sim looks very extensible (there are 'modules' planned for the game, like internet play, controller module etc.), so I could imagine that turning the physics control over to Pontifex when the train enters the bridge isn't that big a problem (it's mostly a problem of 'gluing' the train sim together with Pontifex, and since the train sim already is extensible there's hope for an easy merge).
Anyway I think it could me a lot of fun, and it could make a good foundation for a 2 player co-op game (where one player makes the track in the train sim, the other player makes the bridge), you could make a time limit / money limit etc, 'missions' where you have to connect 2 cities with heavy trains, make multiple bridges in a mountainous terrain via multiple internet players (imagine 8 simultaneous Pontifex players and 1 trainz player building 8 seperate bridges and laying the tracks, for what becomes one complete level with 8 bridges). Then the trainz player have to observe speed limits when driving the train, so the bridge won't collapse because of reckless train driving etc....Add a timelimit to this and you could get into a quite stressfull situation :-)
What I'm basically saying, is I see potential here :-)
Any comments on this idea?