I would estimate no more than 50%. It feels like there are missing things in existing areas (plains instance, mountain crop (maybe onion counts, but is weird), missing recipes (every kind of fish? a higher tier fist weapon? Dark wood walls and floors? Tons more building bits?) even though those areas are 'complete' and function fully, not to mention the not-yet-done biomes. And as popular as it has been, DLC or more after its all said and done as well (?). NONE OF THIS beyond the completion of missing biomes has been promised. This is me taking an educated guess with an optimistic outlook.