Let me respond to the people who are saying get over it and get a new phone already. The W10M user share is abysmally small and MS should really be trying to keep as much of that group as happy as possible. If 50% of the users are using a phone that can't upgrade...again that is 50% less of a user base that developers will to make money off of.
I kept my 1020 updated as long as possible. It was ok on the Insider builds. My hope was that as with most pre-release builds of software, it was more bloated than it needed to be and that MS would optimize it by release time (take out debug/logging code). That is not happening enough to make it a satisfactory experience on some phones. I get it.
So, in response to the Get Over It crowd, I did get a new phone. I got an iPhone 6S+. I believe that the iPhone 4 can still run iOS 9.3 after almost 6 years on the market. Is it a great experience, probably not. Are all of the features there? Nope. But Apple has done a far better job in phone market of creating loyalty even to those people who can't or don't want to upgrade very often. I am not a ****** of any company. I have a Surface Book, the original Surface Pro, L1020, iPhone 6S+, MacBook Pro (2011), iPad Air, some Android tablet that I hate, and some other odds and ends. MS has done a great job of creating loyalty in the PC market but not so much in mobile market where Apple has been the exact opposite (I don't think my Mac Book will supported much longer). If MS is SERIOUS about the mobile market it has to create loyalty. This Get Over It and get a new phone is just wrong. Most people will get a new phone when they want to. If they are told they 'have' to then that's when they start looking around. That's what I did and believe me I really liked Windows Phone (720/920/1020).