Don't Wait If You Can't Wait Until October
If you can't wait another month or two, don't wait for the Pixel 4 or Pixel 4 XL.
The Pixel, Pixel 2, and the latest Pixel 3 all got announced in the first week of October and were released a few weeks later around the end of October, basically November. We still have a little bit of a wait, and leaks suggest an October 7th launch event. However, we're starting to see leaks and FCC certifications, so Google could be planning a September announcement to spoil the iPhone 11 debut.
So, if you're up for an upgrade, have the money now, or need a device within the next few months, don't bother waiting.
Samsung's Galaxy S10 arrived in March, the OnePlus 7 Pro is solid, and both of those could make Google speed up its release. In all likelihood though, it'll arrive at the end of October just like it has for the last 3+ years.