You'll have to either stay on Xbox (presuming your on 360 right now) and upgrade to Xbox One to get the rewards still due to the fact xbox characters do not transfer to playstation.

One possible idea - it says you get the VIP rewards if you own expansions 1 and 2 by August 31. You could go onto the Playstation Store website any time before the end of August and create a profile that you will then use on the PS4 when you get it. Say you were to buy the $60 version that includes Destiny and all the expansions through the store, even though you wouldn't be able to download them yet, it should still count as you owning them by August 31 and count towards the VIP rewards...I think. It's not something I've tried, so I can't be positive, but if you're going to re-buy the game for PS4 anyway it might be worth a try.