I was going to say "Strixhaven doesn't seem to have much for me, but I thought the same about Kaldheim, and I ended up including 15 cards in my cube's core." So I came back to this thread because now I have a way better idea of what Kaldheim has to offer to my cube.
Likely mainstays
The best thing about Kaldheim limited was how fun playing aggro was. This is because the equipment theme, with Runes being an important feature of the format, equipment in general providing a more lasting threat in longer games, equip costs working as a mana sink for using them on offense and defense, and Goldvein Pick enabling splashes in aggressive decks.
Boast also helps with making aggro full of decisions, and Usher is a 2/1 beater primarily, but its ability makes it anything but dumb to play with. The T2 decision of activating it or not is a classic card advantage vs tempo one which we've been missing a lot lately.
Cosmos Elixir has nothing to do with all this, but it's an elegant card that plays well and has so much going for it: it's a lifegain payoff and enabler, it's not terrible when being attacked, it's good when playing against control, and the decision of when to play it is a pretty deep one.
Moderate confidence
These are cards I think have a decent chance to stay for a long time in my cube, but less so than the first ones.
Village Rites is very good against removal, working as both a sacrifice enabler and an aggro-control "protection". It's a little on the weaker side, which is why I don't think it's a slam dunk.
Basalt Ravager is one of the best generic tribal payoffs, and being weaker than Flametongue Kavu is a good thing. It can go to face, which is pretty relevant and sometimes correct, and sandbagging it until you reach a decent amount of the same type makes the card more interesting to play with than Kavu. The extra dimension of caring about tribal to drafting is very welcome. I love the card, but Basalt Ravager is also on the weaker side, though.
Rune of Speed is part of the equipment direction to which I'm taking my artifacts archetype. It's probably the third best rune, but it's in the right color. Also have power level concerns with it.
Elvish Warmaster is an elf lord that doesn't just pump all elves and isn't too explosive. The activated ability isn't relevant in most games, but it puts pressure on the opponent and when it's relevant, it is very relevant. It's a bit inelegant though.
Masked Vandal is a changeling, and with the tribal component it's great to have any playable changeling. Artifact/enchantment removal is really good in my cube, and I'm pretty confident the card is good enough, but the reservation here is that the ability "cost" is unintuitive.
Maskwood Nexus is an awesome bridge that ties together all those tribal synergies in my cube. The problem is being so slow against aggro.
Probably just passing by
The concern with all those is power level / excitement. They play well in retail limited and fill important roles, but people have to actually maindeck them.