I think that this found will improve the chance for a startup to become big, because with this extra money they can focus on the product and have a bigger found for advertising. If YC dose this is a win win situation for them because the companies that they found will get a bigger evaluation from the start. So now they invest $20K (let's say) and get somewhere to 10% if they invest $150K and still get 10% the company is worth $1.5 mil from the start not $200.000 like in the current funding.
Finding follow-on money for YC companies with a product and a plan was not difficult in the past, it just got a bit easier but not even that much. The YC brand is pretty strong and more or less guarantees investor interest. The only big difference here is that this guy basically won't say 'no'.
