I managed to get the gold iphone 5s at launch day but only because I got it from a re-contract with my carrier. Also, the carriers don't sell off contract iphones for pretty much the first few batches because they are in such short supply, and the priority goes to those who are signing 2 years contract. :/ If not there is no chance in hell I could get one from the online store (no apple stores here, only authorised retailers), which doesn't stock the new iphones until a month or 2 later.
I was lucky in that my carrier kept things really organised, just needed to pre-register what I want, and on the launch itself, i just drop by at the time frame I chose, and then collect and pay for the phone I chose (colour/storage) when registering. Hassle-free and no need to queue overnight or whatsoever. Just need to have a fast internet access and fast fingers to reserve the phone online (the gold one sold out in minutes after registration opened).
Where I live, the iPhones are bound to sell out no matter what. We're part of the first wave of release for the past couple of generations of iPhones now, and all phones sold here has to be unlocked by law (yes, even if you sign a 2 year contract with the carrier), so there is high demand from exporters who will buy in large quantities of iPhones to sell it at a profit to countries who aren't part of the first wave of release. Which drives up the prices of the phone as well. I've seen over 50% markup for the off-contract Gold iphone 5s at launch, it's insanity. Even when apple online store starts selling it, it's almost always out of stock since people will buy as much as they can to again, export.
So yeah, i think no matter what, there will be availability problems. Especially when it's a brand new design this year with new screen size/sizes. I'll probably skip the iPhone 6 this time round and wait till the 6S. My current yearly upgrade is due in March (all because of the BlackBerry Z10's launch where i live, lol), so it's right smack in the middle between new iphones. I'll just wait another 6 months to get the 6S and push the cycle back to coincide with new iphone launches.