Http://documents.latimes.com/bungie-activision-contract/
This is the contract that was court ordered to be released when activision was sued
Around the end of page 2 and the beginning of page 3 there is the subject of platforms the contract says "destiny #2 will be released to xbox 360 xbox one and personal computers running windows based operating systems" it's right there!
Hope this helps
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unfortunately this is very unlikely since they never mentioned ps4 and I highly doubt they are dumping that market for pc