I do also have seen this warning for one of my Apps, but not for the other, though both do use UIWebView. So this warning might not be simply based on the usage of UIWebView alone, but maybe also some other information, like for example deployment targets and other "invisible" dependencies and maybe it's also a difference if this is a new App or an update...
Right now this really seems to be a warning only, so you probabyl still can get Apps accepted for the AppStore which use UIWebView.
And Apple can't really remove UIWebView from the iOS so easily, probably hundreds of thousands of (older) Apps would no longer work. Though of course they could stop accepting new Apps and updates which use UIWebView. But this can be also difficult because Apps which are supposed to run under older iOS releases (deployment target) might still require UIWebView.
In general I would appreciate if Apple would spend its time to make WKWebView a real replacement for UIWebView instead of forcing us to a WKWebView which still can't do some basic stuff (which would be simple to implement with UIWebView).
- If you need to route the traffic through a proxy, you can't do this with WKWebView.
- If you want to implement an Offline mode, you would need to control and handle the cache, not possible with WKWebView.
- If you need to set custom HTTP headers (for example if you need to enforce "safe search" on youtube in a browser for children, you would have to add a certain HTTP header in all requests), not possible in WKWebView.
- You need a certain cookie accept policy (instead of Apple's proprietary cookie handling, which doesn't work for all sites - even Safari fails on a few web sites because of this), you are out of luck with WKWebView.
- The list can go on forever (almost ;-)...