Love the idea, and the concept sounds great - but in all actuality, these will need to be in stores. Almost every time I've had to buy Solo cups was right before, or during a party with a "Hey, can somebody run and get some Solo cups?" - I can't imagine anybody planning in advance or putting in any more effort than a run to the store... for beer pong.
But, that's not to say these wouldn't be a perfect fit for the right buyers. Maybe professional (semi-professional?) beer pong leagues would need something like this. Keeps the game fair and level, and adds a little depth.
Sidedoor