As the title says, will there be any sort of beta for PC users who preorder or anything like that?

Too early to know I guess...

And why people who preorders should have a demo or whatever and not those who didn′t, people who preorders do it so they can get the bow early and extra skins/dog tags, you don′t need anything else.

Less favouritism in here, either if we get a SP demo, MP or both it has be for everyone to test it and decide if we want to buy it or not.

Haha seriously, the purpose of the demo is to correct issues and have a large number of people reporting bugs, giving feedback and ALSO convincing them to buy the game