I think it's fixed in latest SVN.World_WIP- Archipelago issue on Giant map. SVN 9390. It hangs indefinitely in the "Initialising" stage. Waited 10 mins and had to kill it.
I couldn't reproduce the hang, but I noticed that it in some instances it could take about 20 minutes to create an archipelago map.
I suspect it didn't really hang for you, that it was just doing some wonky math, and eventually would have completed after 15-30 minutes.