Oh make no mistake, I'm on record as not really caring whether we ever see another theatrical Star Trek film. In my opinion, it's a TV franchise at its core, and it can stay there as far as I'm concerned.
But I'm pretty sick of the tedius "will they/won't they" shenanigans at Paramount.
Yeah, my simplified headcanon explanation is that the Kelvin universe was always there, and Spock and Nero happened to tunnel into it.
If you want to add the wrinkle that the red matter implosion somehow created it (which the original film seems to suggest)...well, it's more complicated, but it works, too.