I tend to agree with sianny123 that it's likely a hardware issue.
My warranty replacement 7 Plus has been working fine for 3 weeks now. I never had the wifi issue, only the GPS issue. Before returning the phone, the store went through all of the possible fixes including a factory reset and changing the SIM card.
I assume Apple has looked at my returned phone and other returned phones and may have figured out the problem by now. Sadly, I think those phones that are out of warranty may be out of luck. I don't see Apple replacing them for free but, who knows, maybe they'll surprise us.
If your phone is having this problem and is still in warranty, I'd get it replaced before your warranty expires instead of waiting for an IOS update to fix the problem.
My wife's iPhone 6 has been working fine so far which is good since it's out of warranty. If it develops the same problem we are all having, we will replace it either with an Android phone with extended warranty or an iPhone with extended warranty.
It would be nice if Apple would acknowledge the problem. Even coming out and saying, "Yes, we are aware of the problem, your phone can't be fixed, and we're not going to replace any phones" is better than just leaving us in the dark. At least we'd know what our next step would be.
Good luck to all. This is a very frustrating problem.