I think it's a bit wishful thinking to have every user upgrade to new Windows just because rF2 says so. rF2 only ditched Win XP support a year or two ago when the usergroup became marginal. According to this wiki page there are currently two or three games in the whole world with DX12 support, which tells a bit about how the gaming industry considers DX12. It would be a marketing suicide for ISI to ditch legacy DX support and move to DX12 solely, there is no other way of putting it. To work around this issue, they would have to re-code the game both for DX11 and DX12, or somehow combine DX9 and DX12 support which would probably be the first game engine in the world to do it.