I think the priize pools will continue to increase as more players get involved, but I can't imagine the buyins getting to much bigger for the main events. As the odds of a good player outlasting a field get longer, the investment vs reward starts to get murky even for the best players.
Also, 10,000 is a lot for online sites to compensate for. If it became 50,000 only the sites with the most traffic could guarentee seats without looking to take a hit if not enough players show up/qualify. Not saying the online sites are strapped for cash or anything
, just that they make a good deal off of the qualifier tourneys now, if they quintupled the buyins, less players can afford it, so they might end up not making AS MUCH.
It will be interesting to see (and play through) the next year or two and see how these things shake out....