No idea on release other than "2020".
What's been shown so far has been described as "pre-alpha" and sending that out to testers has been delayed by over a month so far due to an issue with compiling the latest build (we believe it's finally been sent out, at least in a phased manner). Once feedback is collected, acted upon and a new build compiled, it will go out to a second round of testing. Will it still be considered a pre-alpha, and alpha or a beta by then, who knows? Assuming a further round of fixing, recompiling, etc. happens and then another round of testing. Then there's the final touch ups, regionalising, preparing for distribution, marketing wind-up, etc. It will likely all take quite some time, hence they've not specified a half or quarter for 2020. The only thing in its favour is that it's supported by Microsoft, but then again there are a number of cross department dependencies (Bing maps, Azure AI and distribution, Asobo, etc.).
So if you expect it to be released right at the squeeky end of 2020 and it comes earlier, we can all be pleasantly surprised.