Fragility could really be side stepped with the introduction of carbon fiber chassis and body components as well as gorilla glass enhancements that have been discussed over the last year or so. Truth be told, you could have a device this thin with characteristics and durability BETTER than the current offerings on the market. The technology has long been out there, it just comes down to implementing it.
Where my concern would be is the battery life...so far we've not seen any real world testing on thinner batteries (than what we have already) that support long life spans, so I would be concerned that this sexy phone would also only get 2-3 hours of full battery life.