I assume it can still drop if you don´t pre-order. Pre-ordering just gives it to you right away.
It looks good but I really wish they would figure out how to offer more strikes.
It's not even hard.
TTK had some absolute awesome story missions that could have been easily retooled as strikes. I really can't figure out why they wouldn't do that. It just makes no sense to me.
That story mission where you fight a Oryx Wraith or whatever they are called on top of that citadel level? That would make a great Strike! But nope, it's just stuck as a story mission with crappy rewards so no reason to play it more than once!
My guess is that normal Year 2 Ballerhorns will be introduced and drop normally, but the Iron Ballerhorn will always be an exclusive skin.