It looks like the new Team Fortress 2 update has just gone live, and it seems that the Soldier and Demoman will indeed be competing with each other.

Along with the new weapon being revealed each day for each class, a la the Spy vs Sniper update, the class with the most kills against the opposing class  (Soldier > Demoman and vice versa) will be getting a super special top secret weapon at the end of the competition.

So get to the killing people, make my Demoman proud and kill some Soldiers for me!

The War Update (TeamFortress.com)