I plan on keeping my 5S, as I am under contract until next September and I am keeping my grandfathered plan features. Only way I might be tempted would be if the 5.5" phone happens to be true and is made of sapphire and has retina display.
But I'm among the skeptics who are not convinced that it will be released in the near future. Plus, I've been on the "S" cycle since the 3GS and I don't plan on deviating from that now. I actually prefer "S" cycle models as they seem to have better longevity and are more capable of handling future iOS updates than non "S" models.
The 3G, which technically was able to "support" iOS 4, got brought to its knees by iOS 4 whereas the 3GS was good up through iOS 6.
Likewise the 4 was technically capable of "supporting" iOS 7 but the lag times rendered the phone virtually inoperable in many instances.
Hopefully the 5/5C won't encounter similar issues of lag when running iOS 8. But time will tell.
I guess my point being that the "S" cycle phones seem to be better at handling iOS updates they are supposed to be capable of supporting than non-"S" cycle phones seem to be.
I'm good keeping my 5S and looking forward to iOS 8. If I had opted for the 5C (which I wasn't going to!) then I would be looking to upgrade, as the A6 devices won't likely run iOS 8 as smoothly nor will they be able to take advantage of all the features. By time I'm due for an upgrade, the 6S will be on the horizon and I will be ready.