D's right, a huge chunk of 0.10.0's existence will be do add bosses, as well more general type NPCs to make the worlds more alive.
That being said, the "generate once per world" part I am kind of against for several reasons, including how awfully those would fit with everything else in the world, and with how impossible it'll be to correctly fit some of them considering there are multiple bosses per structure.
For islands that's already a thing, there is a config which allows a range of min/max for the size of islands, it still be help as much as a regular world, simple because of the general lack of ground, but islands with the max size (10) will be quite huge and so allow for more chances when it comes to structures.
I'll look into it and see if its possible to add some form of support for simple voice chat.