It is nothing like the DKs. The DKs offered (usually) "infinite" value through the combination of their hero power and battlecry. Zeph is a single tempo swing. It's a great one. But it's also incredibly conditional.
This whole discussion about class identity as it relates to Zephyrs is really flimsy. That's what neutral cards always do and have always done. Zeph just kicks it up a notch in very specific situations.
Rogue and Warlock "don't have heal," but there's lots of heal in neutral. Some decks "don't have taunt," but there's lots of taunt in neutral. Some classes don't have much draw, but there's lots of draw in neutral. Etc.
Zeph is no different than any of this. You guys just don't like it because it's ending a game you were unable to win before he came down. Similar shit could could be said about a vast number of cards in the past and going forward.
In a lot of ways he's an omni-tech card. That's really good. It's incredibly powerful. But the cost you're paying is that you're a highlander deck, or you are at the very end of your game.
That flexibility is so crazy that it's a foregone conclusion... OF COURSE every deck is going to start including it.
I am doubtful that this will be the case. However, even if it does occur that every single deck plays this card, I don't think it will matter for most decks.
Hypothetically, let's say that every aggro deck starts to include this as a hail mary of sorts, as the OP suggests. It's only effective so late into the game that it's impact should be fairly negligible.
If you're a control deck against an aggro deck, you've won or lost long before Zeph is active. If you can't survive one tempo switch, what the fuck were you doing all of the turns after you stabilized?
If you're control vs. control these kind of swings are the bread and butter of control matchups. It might suck a little, but it's certainly not anything we aren't used to. It's not unreasonable to ask someone to be prepared for it in these instances.
There are the strange non-highlander decks where Zeph works, but I think those are examples of good uses of the card. It's cool that Myra's can use Zeph, and that Druid draws so quickly that Zeph is active, or that Tip the Scales thins your deck so greatly that Zeph is playable early in the game. Those are neat, smart uses for the card.
Sure, maybe we see every deck include Zeph at some point. But most the times, it'll be Bloodfen Raptor. I think overtime, people will realize that's not worth it in most instances.
I think we can all agree that Keleseth was an abomination, especially in Rogue.
Your comparison to the Lich King is a good one; to me, that card is a perfect example as to how the process of design should go. However, Lich King had clear downsides to it, when compared to Zephrys. Half of the cards where mostly bad in most situations, and it was at random. Apart from that, it was an 8-mana card. Zephrys lets you choose, and with the constant tweaking of the card, its outcomes will only get better.
I disagree. Yes, sometimes the lich cards were bad, but Lich King was always an 8-mana, 8/8, taunt that drew a card.
In non-highlander decks, you aren't playing Zeph on curve and getting his effect. Even though the effect is much better, you are playing it at the very end of the game. Which means you've been holding a dead card in your hand for a very long time. It's not entirely unlike Nomi in that respect.
Where Lich King pretty much fit in everything, I think it's likely that non-Highlander decks playing Zeph will have to be pretty unique. Not every deck has Myra's or Tip the Scales to activate Zeph easily. For example, you aren't putting this in non-highlander Aggro Warrior (probably????).