Wait for more Call of Duty: Modern Warfare Information
The biggest reason not to pre-order Call of Duty: Modern Warfare yet is that we don't know everything yet.
With Modern Warfare there is no Season Pass, so this will also be a new way for Call of Duty Points to play into the mix and for us to see how many new maps and free DLC options we get.
Activision revealed many of the Battle Pass details today, but we still don't know how much it costs and exactly how long a Battle Pass will last. Activision is launching the first one later this year, so you likely won't know all the details until post-release. We also don't know yet if there will be hardcore modes available at launch.
Don't pre-order Call of Duty: Modern Warfare with missing information. Wait and make Activision earn your money, especially if you plan to buy digitally.