I'm not sure how the incentives will play out. It takes $60k at the time of writing to become a validator, and they've yet to implement the mechanism to exit your stake; so I think there will be some hesitancy to become one. The more validators there are, the worse odds that yours will be chosen to handle a block; and I believe as the number of validators increases the reward per block also decreases (though it's been a while since I read the proposal).