well, the islands can be as big as 6×6 to  more than 200 blocks on surface. i say that the border should be very big, considering that there are end dungeons. something will have to be done about the chorus plants as well, if u have been in the snapshot u know what i mean 🙂 also i know for a fact that the end will not be pretty because of said islands because, well, they are islands with the Void as water-