Given the development process for Windows 10 May 2004 (the 20H1 feature update) ended back in December 2019, there isn't a whole lot new to say about the 2004 update. Since December, Microsoft has made numerous tweaks, updates, and fixes to 2004, but no new features have been added to it. In theory, at least, this should mean smooth sailing for those updating to the new feature release, given it has had nearly six months of additional testing by Insiders before today's release kick-off.
Starting today, Microsoft is making 2004 available to "seekers, " meaning those who proactive go to Windows Updates, check for updates, and subsequently opt to download it immediately. As it has been doing with recent updates, Microsoft will be throttling delivery, providing the new feature update over the next few weeks to users with devices that Microsoft has deemed most likely to accommodate the 2004 feature update successfully.
Microsoft already has been testing via the Fast Ring new features which may or may not end up in Windows 10 20H2. My sources have said that Microsoft is planning to make the 20H2 build a small, incremental update to 2004 -- the same way that 1909 was a cumulative-update-like experience to 1903. Microsoft officials have not said this publicly, however. The 20H2 update, codenamed "Manganese," should be available this fall, if Microsoft sticks to its normal rollout cadence. Fast Ring testers should begin to see builds of 21H1 (codenamed "Iron") starting later in June 2020.