I definitely don't believe that today and I doubt it will ever come to pass. There are more cash-efficient ways to influence elections than warping betting odds, and I think that will hold true no matter how large the betting market gets because the manipulation gets more expensive as the market gets more attention.

The weaker form of your argument "Without the caps it's biased toward people who can make big bets" is the entire point of a betting market.

Edit: The one edge case where it might happen is precisely this article. Buying your way to say 5% after some organic positive press might be an effective way to buy buzz at relatively low cost. It's a small one time boost for a campaign though.