Jokes about 80s cellphones vs smartphones, crude PC's vs the internet, stalking and other teen sex comedy shenanigans being legal, push it a few years later for Trump is president (the businessmen! Of course, money is important and you need a lot of it if you want to be President), jokes regarding the lack of politically correct culture as well as the need for safe spaces, mocking rampant materialism and strange clothing styles as well as the idealism which is lacking today. Would practically write itself. The terrorists would likely have to go; hard to keep that joke today with the numerous attacks and sensitivity around that issue, though the War on Terror could cause Doc pause regarding the future and Marty maybe not wanting to return.