Sure it can be countered.
I think it's highly unlikely we get this, though, because of the game design.
"How many times would you like to activate that?"
"oh, just one. for now." figure out mana selection for just one shot of whatever you're using.
... watch the timer go down. Ability resolves.
timer starts again for the phase. pause it. activate ability again. dialog to ask how many times. watch the timer start for responses again.
repeat. repeat.
Not that I'm saying the developers won't be up to the task, but I'm saying they're trying to make this version of the game play very snappy. This card does not do that in an online game.
Actually, with the auto-resolve option, the programmers may not be up to the task. That's a lot of strange interactions you could get.
I don't think you understand how the card works. It resolves once, and that's it. It exiles everything that is on the stack at the time you cast it. And you don't get to pick and choose, either.
What this does is counter uncounterable stuff, counter abilities including on-cast abilities, and counter multiple spells/abilities in those fringe cases where the opponent puts multiple spells/abilities on the stack instead of resolving them one after the other.
Riiiight... it counters the stack. Not future stuff, not resolved stuff, but the stack.
So I'm pointing out: what's on the stack?
Because of this thing's existence you don't want a lot of stuff on the stack at once. But the game doesn't really lend itself to that.
For example, you don't want to activate
Nantuko Husk again while it's first activation is on the stack. Because then the opponent can counter both of them at once with one card. You activate it once, *resolve it*, then activate it again. But that's watching the timer a lot and stopping it a lot - you need the timer to fully tick down for possible responses to each activation, not just to the end result.
Or something like
Ember-Eye Wolf where each activation also needs to nitpick the mana selection to not eat up RR when you mean to leave more R for later.
That's what I'm saying. It's a UI issue that in paper play with a human you can address in about half a second, but here need to keep fussing over watching timers. and that's with the developers really concerned with gameplay speed.
It's not that different to paper. Sure paper doesn't have a timer but if this counter turns out good then paper players can also resolve 1 at a time too.