Well, that was fast. Sounds like they may even be serious, too. Increasing from 300 million to over a 1 billion users is a cool feat. In my experience though, it's harder to get the first 300 million (or wherever the tipping point is). You still have to have something to offer and not ruin things, but a lot of the growth starts coming from the product's own inertia.
Now, the announcement doesn't say they're exploring their own blockchain, though that may well be what they're doing. But without that specificity, my guess is they're looking at many blockchains, and if so, eventually, they take a look at STEEM.
I guess it will come down to whether or not it makes sense to them to use their own blockchain, and develop it over a longer period of time (whatever that might be), or decide a little B2B agreement is in order and park themselves with a SMT atop the only socialized blockchain currently running and proven. :)