I'd obviously want a temperate pack for the Tasmanian devil alone, but even discounting them it seems much more appealing to me than any of the other remaining biome options besides islands (which aren't even a biome, they're a landform). Taiga and tundra have basically no animals that interest me, and even highlands is not likely to contain any of the mountain species I'd actually like to see - my most wanted mountain animals are all rocky arid species like the aoudad, yellow-footed rock-wallaby and rock hyrax, but a highlands pack is much more likely to just be another batch of cold climate caprines and carnivorans.
On the other hand, I feel a temperate pack that's something like [Tasmanian devil + wild boar + American black bear + wildcard (pheasant, duck, kiwi, echidna, muntjac, marten, etc)] would be both simple to make and have wide appeal - Australians get their devil, Europeans get their boar, North Americans get their black bear, and the wildcard option has all kinds of potential. There are definitely fewer temperate species high on my personal needs list compared to the tropics and aridlands, but seeing as these two biomes are unlikely to get a revisit within the next few packs it seems like one of the best remaining options for a fall DLC to me.