I started with a case on my 6+ but within a few weeks took it off and have been enjoying the phone without one ever since. This design, in particular, feels so different without a case because the reduced weight and thinness makes it feel less like a "phablet" yet provides all of the advantages of a large screen. It is easier to pocket and use on a daily basis without the case. Also - as you said, it looks fantastic.
After ~7 months of daily use the phone has held up remarkably well. The finish really hides scratches and it looks like new. I have dropped it a few times on carpet, grass/dirt and in the car from a mount/holder to the floormats. Overall, I've found the phone to be very durable. If scuffs and scratches start to appear in the future I'll just chalk it up to adding a layer "character".
Sure, if I were to drop it on a hard surface the screen could shatter or the aluminum case could dent but I've seen and read postings where these things happen to others even while using a reasonably sized case. If I were to wrap it in a case, accidentally drop it and the screen shattered anyway - I would have missed out the enjoyment of using it without a case for nothing. Given that, my thinking was why not enjoy it as it was designed?