Given the facts that...
...at the end of season 1, we were at 6.1 GB; and
...at the end of season 2, we were at 19.5 GB, which means season 2 by itself was 13.4 GB; and
...the episode-to-episode size increase has gone from 3.1 GB to 3.4 GB to 5 GB all within season 2; and
...the interlude all by itself is 2.6 GB, and that's less than 1/5th of the render and animation time of episode 8;
Anybody who thinks that there's more than a snowball's chance in hell that season 4 won't be a separate file from season 3 needs to tell us what they are smoking, because it's some powerful stuff.