First problem I can see is on the random allocation of countries. The odds of different countries winning vary largely, only about 10% of the total countries really stand a good chance of winning, assuming you get the 48 participants, over 40% already know from their picks that they're losing. It's worse now that the tournament has already started and we've seen teams play and lose.
Another format that gives every member an equal chance if winning will be a better approach here.
On the question of interest, I doubt there will be considering the timing. World cup fans are already heavily involved in other pools that were initiated before the tournament even started, you'll knot easily get people to join now after the first round is played.
This was where my attention was drawn to immediately I saw the title and I read through the post to know what the op is about. The timing is late, it is what killed the idea of the thread before the op conceived it.
With the low registration fee of $5 there would have been many forum members who would have declared interest just for entertainment sake before the pool prize. But the world cup has began already and is a week now from the date of the first match of the tournament.
He should just kill the idea, wait for the next world and comeback with something better both in the number of participants which should be reduced and the random allocation mechanism.