IF I play it, it will absolutely be on the PC. I never played the first one because it was on a console. I own the consoles, but I am absolute shit with a shooter on a controller. I gotta have the mouse and keyboard (or mouse and orbweaver in my case).
That being said, I don't know if I will buy it. It all depends on their decisions between now and release. I really like the concept but they really need to fix the complaints that plagued the first one. The glaring errors in judgement they made with destiny 1 just ruined what could have been a beautiful thing.
Honestly, how can you make a RPG without even considering the lessons learned (and are industry standard) in other mmorpgs. Loot, lore, immersive story line, marketplace, trading, and many other issues have already been completely worked out in so many other games. Companies have already figured out what sells and what the consumer wants out of those areas. How can you just ignore all that market research? If they ignore it a second time with Destiny 2, it will definitely be passing on it.
If they do it proper this time though? I will definitely be buying it and playing it for quite a while. I have my hopes. After all, Activision owns Blizzard now. So I can only hope that some of the expertise from Overwatch and WoW will bleed over and we will see some better decision making.