The problem with this is that eBay wishes to provide consumer protections. eBay provides these protections by allowing the seller access to their funds almost immediately, the seller will ship the product, and the buyer will leave positive feedback when they see the product is as advertised. When there is a dispute that is ruled in favor of the buyer then eBay can simply charge back the seller's bank account and reimburse the buyer.
If eBay were to provide the same level of protection it would not be able to release the funds to the seller until a longer time then it can now.
One alternative could be to allow buyers to pay in BTC but eBay would convert the BTC to fiat and pay sellers in fiat. This would mean that eBay would act in a way that is little different then an exchange.
This is simply not true. For example, you pay me $20 for a stick of RAM. The funds are immediately "available". I walk down to the atm with my PayPal debit card, and pull the $20 out in cash. My account is now at $0. You decide the RAM is not what I promised, and complain. Paypal reverses that charge, leaving my account $-20. Only problem is I still have a $20 bill in my pocket. This is no different than if I took the $20 out in BTC. PayPal would still make my account $-20.
What paypal has to figure is how to let people use bitcoin, without people deciding to go around their system. There is a lot to consider here. Paypal could limit their integration with bitcoin simply to withdrawals, and not let you actually denominate your account in BTC. They could also become a full wallet. They would control the private key, and still act as an escrow and take their cut. They could even allow direct btc to btc payments, similar to how "friends and family" no charge payments are already done. No escrow, no fee. Bitcoin is a risk to paypals empire, and they know it. They know bitcoin is likely unstoppable. They can only hope to be the first major bitcoin payment provider to market. They still have time, but they have to beat out google and amazon. They know this as well. That's why it will be done, and it will be soon. This year. Paypal doesn't have to be early, just before another major player. It would not surprise me if they have fully functional bitcoin support in alpha. Exciting times guys.
BTC etc works outside the legal system in a gray area. So you have to clean out your bank account for your scenario to work and you would have to continue to have that account in the negative. If your bank covered the overdraft, then you'll owe your bank. This will follow you around until you clear it up.
I agree about the rest though. The chances of this stuff happening are near 0. Paypal has a monopoly of fees. Giving BTC credibility does little but undermine their business longterm. Ebay doesn't sell things, they are middlemen who collect fees. What little business they gain from BTC they pay for in a whole slew of other areas.