Being able to point your users to an update to fix their problems when they come to you for support, or when they go to write an angry review that their app is crashing but they see “iOS 14 support” at the top of the app’s page, is likely to help there. Especially since the earliest adopters are frequently technically competent enough to do that but also frequently demanding enough that their apps work on day one.

So, maybe you can get to it in a couple of days. Fix what you can using the old SDK before GM build becomes available. Then you have a small amount of updates once apps using the new SDK can be submitted. The app will be temporarily broken for a few days on a brand new OS until the update goes live. Is that really a big deal? The world doesn't come to an end if you get a few bad reviews from impatient users. I remember being in the mobile app development rat race and am so glad I left that world behind. Too much daily panic about things that really don't matter much.

Ok, but surely you can understand why people would be upset with Apple for doing this when they had no reason to do so?