When I got on my computer this morning, I saw the dialog that I wouldn't be able to update the Safari Preview that I've been using as my default browser.
I'm not too surprised as WWDC is next week and my Mid-2010 iMac cannot run Mojave and certainly won't be able to run whatever else is coming down the pipe.
I had just hoped that I would have more time to enjoy the new features since I can't get it running on my laptop.
For me, this is a causes a wedge between me and Apple.
Other browsers, such as Firefox, allow you to have access to newer builds regardless of what OS you are running.