I went ahead and ordered a bunch of cases for both the Galaxy Note 5 and the S6 Edge Plus to see what I would get. I'll have a look at these cases in time, but what is more telling is their shipping dates.
One Note 5 case has already left the warehouse and is on it's way. It was a good deal, only 99p with free shipping with a normal price of £25.99, so if you intend to get a Note 5 I'd head on over to Amazon pronto. To me this signals that the Note 5 will be our treat on August 13th. The other cases are also on their way, a good sign for a near release. I expect them to be available that day myself, but Samsung haven't had a same day release of a top tier model before.
The S6 Edge Plus cases have not been so lucky. They're still not in stock with the sellers on Amazon, despite me ordering from a supplier claiming they "Only had 6 left in stock". They're universally the same at this point, but again, cheap. I'd get orders in soon as well if the Edge Plus is what you intend to upgrade to. One supplier marked their offering as dispatched this afternoon, then emailed me a retraction later on saying they wouldn't have any until mid-September.
So after all that, the Note 5 will be released shortly but we're going to be in for a longer wait for the S6 Edge Plus. I expect it will be announced - why not after all these leaks - and coming alongside the Note 5 it'll double the hype and provide Samsung a boost similar to that Motorola experienced last week.