I'm a heavy user of TestFlight. Both personally, and in my day job. The news of TestFlight's parent company Burstly suddenly being bought by Apple is intriguing as it is worrisome.
You can still login, still register a new account. No news on the TestFlight website at all. Other than a help article titled "Android End of Life", indicating they were focusing on just iOS. There goes the ability to use TestFlight for developing and shipping betas on the two most popular mobile platforms. Now you'll have to look elsewhere for app distribution for multiple mobile platforms.
Update: Apple spokesperson Kristin Huguet provided the following, which is as close to a confirmation as Apple ever gets:
"Apple buys smaller technology companies from time to time, and we generally do not discuss our purpose or plans."
I see it going one of two ways:
Apple kills TestFlight as a product. The engineers at TestFlight are simply acqui-hired. Perhaps the engineers don't even stay together as a group, but go work for different teams within Apple.
We luck out, Apple takes the TestFlight team, and their tech, and rolls it into the Apple Developer Portal, and makes our lives easier, as iOS developers.
I'm hoping for scenario #2.