The success of failure of this is going to depend on buyer reception more than anything else, because there will always be businesses willing to meet a demand. 

It's no secret that the "prime" service available eslewhere is often the main reason people shop there, which provides free 2 day shipping if I'm not mistaken, and generally compensates if it's not provided. Of course things that qualify for that have to be dispatched by the company, not individual sellers, and eBay is unlikely to ever invest in that kind of infrastructure.

I checked my main selling category (Jewellery & Watches) - currently there is a little under 5 million listings under the main category. I refined it to show items that had guaranteed delivery within 4 days, and it went down to just a bit over 13 thousand - obviously along with sellers who didn't opt in, this immediately eliminates pretty much all overseas sellers (extra bonus for shoppers who want to both refine searches to Oz only, and exclude sellers who only claim the item is located in Aus), so as much as I dislike the idea as a seller and am unlikely to ever particpate, the appeal to shoppers is undeniable.