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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Also in that contract it stated that Destiny was to be Xbox only the first game, so parts of it have changed since the suit. Don't take it for granted until it's officially announced. That being said it most likely will be, if for nothing more than to make up for those that will not be purchasing the sequel.