Depends on circumstances in the near future I guess? I no expert, but Estonia already wants the NATO to arm up and defend borders cause they feel threatened. So when every of the NATO nation behaves on the contract, they would need to defend the borders. And basically as soon as one missle, projectile or grenade lands on one of the NATOs territory they should move in. But, since most the nations try to avoid an actual world war it's hard to say. I'd say it's more likely than ever before and could happend at one moment to the other. Also America kinda plays a big role in that since they can "force" the NATO to act.

But let's hope for the best