...that said, I bet 1st May is 3850x announcement rather than release
This is what I'm anticipating. May 1st is AMD's anniversary, so the 3850X will be announced on that day, but I'd be confident in saying they'd want to tie its release with the new X570 boards so you have all the top-end shiny at the same time. The leaked Gigabyte slide stated X570 is launching at Computex, which is the end of May. May is still the anniversary month though, so it still works.
That being said though, the Gigabyte slide said "Matisse" is an "all PCIe Gen4 solution" so we'd need new boards to full support it, but I can't quite see AMD wanting a few month gap between Ryzen 3000 landing and actually being able to use it to its fullest (although we'd need PCI-E 4 cards too). I personally think that Gigabyte slide is quite old now (pre June 2018) so it's nice to think the board release has been moved forward, rather than Ryzen 3000 release is May/June.