I asked the kids what they thought about this and no one knew anything (well the girl not knowing didn't surprise me, she's only recently gotten back into roleplaying, her last time was when she was 6, the boys maybe just didn't look into that bit of dndbeyond as most of what they use it for is character creation).
Youngest went and had a look as he's the one with the obsession and he couldn't find it, then got distracted by Spelljammer XD
So the playtest stuff is not integrated into the character builder unless someone adds it to the Homebrew section, which I wouldn't be surprised if someone has already started do just that. Its just the PDF doc that you have to download.
What does the youngest think of Spelljammer?
He thinks it looks cool but I don't know if he's able to read it (if it's free he might but if not then unlikely).