I worked on the Horizon team, and there's only so much I'm comfortable saying, but I can say the team burnt me out and I quit.

There isn't a 100% chance that Beat Saber 2 will be exclusive, but you're right that it's likely and if that happens it will be a shame. My hope is that Facebook moving away from PC VR as a focus means they won't see it as competition, and start releasing previously exclusive games on Steam in the same way Microsoft and Sony have started releasing previously console exclusive titles, but I won't hold my breath.