If we ever get to the point where the blockchain can't handle it what will WDC be worth at that point? and how great is the incentive at that point to solve the problem?
There will be no incentive because there won't be a problem. The blockchain is not a cash register and will never be used en-masse to support point of sale payments in any crypto currency. That isn't it's purpose.
So whether a coin has a 30 second or 10 minute transaction time is irrelevant to it's suitability for use at the point of sale in a retail (in shop or online) environment.