I don't think we have any "absolute" mammals that are "for sure" to get included anymore - I honestly feel like the last two of those were taken care of with the Conservation pack. Of course, others may have a different view.
Highly requested mammals? Sure, and I do think the Tasmanian Devil's sat where it's sat on the meta-list for so long, and has enough community support, that's it's extremely likely we'll get it, but I could also see them possibly ending the game without it. At some point, they have to draw the line, restructure and move on, likely in a trickle from one project to the next instead of one whole leap.
I still hope very strongly for the Wolverine and the Tasmanian Devil. But the were never in my "must haves" which I'm thankful all mammals in that are in the game. I don't feel like they're in the game's must haves either, not if you look at the entire history of what animals were wanted for the zoo. Very few people probably came right out at launch and said "wait, where's the Tasmanian Devil (or Wolverine, or Coati etc). Nope, it was: Where's the Leopard....no Penguin? no meerkat or kangaroo - and two themes that continue through to today, where are the marine animals, and where are (more) birds?
Yes, I'm sure some people were talking about the Wolverine and Devil from the start. I'm sure some people were also talking about the Pacarana and Kit Fox too....just nowhere near enough to claim a large amount of support. We're only at the point we're at now with the Devil and Wolverine because everything that was generally deemed more important has already made it in.
ETA: Hot take: The Tasmanian Devil and Wolverine were not really all that popular for inclusions at launch, and they're only "highly requested" now because Frontier has hit all the necessary points already, at least mammal wise. Sigh excepting more New World Monkeys, which by the discussion around them, it would seem they should be higher up on the lists than they actually are.