Damn, that's a shame. I was expecting Simona to be matched with the Goblin Lord, since she was the next person in the game's narrative line that isn't a DLC character. If that were combined with a sixth episode showing a Shaman, then that would have covered all the different goblin types.
They seemed on a steady course and pattern to give one episode to each goblin type at least, given that's one dimension to the scene variation in the base game (or in hindsight, they did skip the Shaman in the order the goblins are usually presented in-Shaman is between Hobgoblins and Champions, who were Episode 2 and 3-so maybe we can take that as evidence of a preexisting plan to cut it off with Sayuki and Episode 4).
My guess as to why is that the Goblin Lord requires full-on voice acting that the base game doesn't provide and would require an original creation. Not to mention the Shaman is super tricky: either they go with the weakening spell and it's not that unique, or they go with the illusion spell and that's probably incredibly complex for similar reasons to the Goblin Lord's voice (relatively speaking for this sort of media). Oh, and both require elaborate magical circles that are one thing to draw but likely hell to animate.
I don't know how much MyAnimeList can be trusted with this, or where they source this information from, but I hope (or cope, whichever it is) that it's wrong. Or maybe, if I can really cope here, Ill Bourne might get an adaptation down the line.