From what I have seen so far, he has very nice babies, so I doubt it will go down. The mare owning investors know they can make the stud fee back on the sale of the foals, so they will pay it, plus the status of owning a Totilas baby.
It will be interesting to see if his babies are good producers; that's many years down the road, of course.
It would be great if he was not only a great performance horse, but a super sire as well!
As far as going up, I don't know if they could reasonably charge any more without more proof he's a great sire.
More than likely it will either stay the same or go up. It could depend on how busy they want the stallion to be, and also depends what happens at the Olympics. If he earns a top 10 individual finishing, along with the very likely team medal, it is probable/realistic his fee will go up.
On the other hand, Paul is a very shrewd business man. He knows there is a fine balance between pricing a stud fee so that you have 100+ mare owners calling... and pricing it so high such that only 20-50 mare owners come calling. The former at a lower price is earning more money than even a higher-priced latter.
At 5000 euro, and sold 300 doses, you've earned a 1.5 million euro in fees.
If you raise the fee to 10,000 and only get 100 doses sold, you've earned 1 million euro, still a lot of money, but you have actually lost income.
It could also depend what the future plans are for the stallion after London 2012. If they plan on retiring Toto after this being at the top of his game, they won't mind how busy he is and could very well keep the pricing where it is.
If, however, they want him to keep performing, raising the fee to lessen his breeding burden might actually be a wise plan.