On the Future of the Fortress thread, Toady posted a bunch of replies, one that should be interesting for this thread :
http://www.bay12forums.com/smf/index.php?topic=140544.msg6345218#msg6345218 In current version while megabeast/undead can still come, when playing Fortress mode goblin sieges (extremely) rarely happen and sometime not at all in dozen of years of fortress running. Will this be improved in the upcoming version ? or will all those multi-species mixing in fort will make goblin siege even less likely ?
There was one pathing error that has been fixed for the next version that should improve the frequencies in some cases (some mountain embarks). We'll have to see where it goes from there. The species mixing doesn't change anything.
8th year summer in my fortress, and since the 2 sieges of the 7th year, there have been no gob coming to siege
My fort is much more wealthy than last year (non-stop legendary crafter working can do that), has more artifacts/named weapons , and piles of gobs/trolls remains in my self dug catacombs as a reminder that no living gob will manage to break our fort, only dead gobs will get in buried down there, i was expecting more sieges but nothing.
I had a human diplomat that came, the human had their civs in very bad shape in my world, i am surprised the gobs didn't finished them yet.
The thing is that this diplomat was a vampire
that wasn't even hiding the fact he was one.
No unholy monster will be allowed in dwarven homes, my military destroyed this beast.
Considering he was not a hidden vampire, it means the humans knew and were accomplice to that evil, they will certainly come now to try to avenge their master definitive death,, but they will know they have choosen to follow that beast very unwisely when they'll face my legendary full armored squads (8 years of training do that too).