I wonder if WotC will try and stop others using DnDBeyond in such a way, i.e., no one will be able pull the data into their own product. Unless they offer a vastly superior product, I suspect many would just stick with Above VTT and other products that are free.
WotC don't own DNDBeyond.
They have relatively little control over it, because the contracts are already written, and they clearly don't include blocking secondary data usage, as Beyond20 and so on already do that as well.
So they couldn't do that.
As for sticking with their product, yeah, that is likely, but WotC are playing the long game here. They're not expecting everyone to instantly flip from DNDBeyond to their product. They'll likely offer incentives to us their product, whilst they build it up. It would not be hard to offer a superior product to DNDBeyond, frankly, much as I like it. Building a better core system and investing more in it's development (which would still be cheap) would let you exceed their capabilities in short order. On top of that, WotC stuff could be guaranteed to be fully functional day 1 of release, which isn't the case with DNDBeyond (for example, Supernatural Gifts from Theros and Dark Gifts from Ravenloft still don't work on Beyond).
And if they really are planning a new edition in the next few years, which I think they are, they could even playtest it via their new site - it would give them a level of direct feedback never seen before with playtesting. This would be both helpful for development purposes and in getting people moved to the site. Then when 6E or w/e comes out, you have people already using it, and whilst DNDBeyond etc. will be scrambling to accommodate all of 6E's features well, 6E will likely be designed specifically to work perfectly with WotC's own site. And as people are buying new books anyway, why not switch to WotC's official approach?