Paid beta is just "early access", which is fine and it's a good idea to build up hype before they put the "released" tag on it and ship discs in retail stores. But because this game will heavily rely on the servers, it will make a lot of sense to have some open Insider preview weekends, to try to break their servers with a rush of people downloading and playing.
Anyway, on the subject, a late 2020 release seems realistic based on everything I've seen. But with the current pandemic situation, I'd question whether the developers are running at the same pace as they were several months ago. They may need a lot more time to finish some systems and do art passes. I won't be surprised at all if it slips into 2021. If Microsoft gets this game right, it's easily going to be a PC system seller, and likely garner millions of sales for years to come. The Microsoft of today won't let this one flop like the previous attempt under old management, and an extra year with the bun in the oven is not going to hurt their financials.