Goblin ambushes, yes. Hopefully coming up in Improved Sieges right after Steam. The Ambusher tag ambushes are beautiful when they actually throw up a plausible ambush.
... From an average player's point of view trying to enjoy the game as it currently is: a feature was in the game and worked fine, then it got broken, then it got removed, but don't worry, it'll be reintroduced in a better way two years from now (at least). .... I have a hard time imagining that a Steam customer being freshly introduced would interpret it as anything other than a net loss in features.
You know the last time features went "missing" was in 2012 right? When the game was rewritten to be more of a living world simulator. And since then they haven't, right?
The ambush event is a pretty clear feature loss. I think we can all acknowledge the current "living" world frequently doesn't do as good a job of delivering a progression of invaders as the old system, and in DF-development time, 2012 isn't that long ago.

Every time I pick up the game, I'm reminded of how I see less invader activity than the pre-world-activation version.
But, as you point out, DF is a simulator and gameplay is emergent from that. (With the entire game in all its craziness as the evidence that someday, more cool things will happen.)
Dwarf Fortress won't ever be "a game" unless Kitfox go out of their way to break it completely and try to make a generic site management sim out of it. It's not that, it's something unique. .... Dumbing down the game, stopping development and abandoning the vision will kill Dwarf Fortress ...
I think it can be a good game and not hurt the vision. It won't dumb down the game for Toady to pay some more attention to gameplay for gameplay's sake once or twice a decade.
In a similar vein, DF isn't THAT hard or cerebral a game. Most of the hurdle to new players is the user interface. I don't think it's a reasonable ask right now, but someday it will be worth it to decouple the simulator and the SDL graphics hooks and make a full UI redesign doable. Probably the main reason it hasn't been worth it so far is the stress it would cause Toady to have to work with a team. He's cited the risk of a third-party UI creating a support load as a reason he hasn't done it in the past. It's hard to tell how far the Kitfox partnership will go in that vein, but anything is a start.
-- Create a demonic fortress somewhere within the selected embark location
-- author: Atomic Chicken
...
I was skimming a bit and after misreading the header comment, started reading fast thinking "It creates an ATOMIC CHICKEN!?! How???"
Then I went back up and realized it doesn't actually add Atomic Chickens to the game.