The "this kind of data" you're worried about is not the biometric data giving the precise geometry of your face, as used by Face ID.Even if all developers stick to the strict Apple rules about this, what will happen if some of them get hacked and all the data is stolen? I mean this is quite a big possibility, especially since many developers do not have some "Top graded anti-NSA/breach" security on their servers.
Apple should never allow anyone to have access to this kind of data.
Rather, it's your expression - user is smiling, user is raising an eyebrow, user blinked. If some of the developers get hacked and the data is stolen, some evil third party could find out that you once smiled. Are you still as concerned?
There are some privacy concerns related to programs monitoring in real time how you're reacting to something like an ad, but there's little point in a developer uploading and storing "user smiled and then blinked twice" - what they'd be interested in is "user had a positive reaction to the ad or feature that was on screen at that time".
The concern would be more along the lines of: imagine a F2P game that lets one get magic coins in exchange for watching ads, what if now the app paused the ad and refused to unpause it unless/until you were actually staring at the screen, and also recorded their guess at whether you liked or disliked the ad (based on combinations of "did user raise an eyebrow", "did user smile", etc.). That would fall somewhere on the annoying/worrisome/creepy end of the scale. And these are the actions that are prevented only by Apple saying they're going to look for software doing that and not let it through their software testing process.
Note that much of this could be done already, by any app that requests access to the camera - Apple's new frameworks just do the ground work of recognizing things like "user is smiling" without every developer having to reinvent that wheel using raw camera images. There's nothing right now to prevent developers from taking pictures of you and uploading them - if you've given the app access to your camera - other than Apple checking your app for code that does that.
The article seems fairly clear that this (gauging user reactions to on-screen content) is the issue at hand, but some people still seem to running around worrying because they've conflated this with concerns that user's biometric recognition data could be uploaded to servers (otherwise the "on noes, what if third-party servers are breached" line of reasoning is nonsensical) - this is not the issue (the high-res biometric data can't leave the iPhone, just as your fingerprint can't, with TouchID).
(As someone pointed out recently, a bigger concern would be if some company could get access to all your photos, and upload them to their servers, and use ever-improving software on their high-powered servers to sift through all your photos with facial-, scene-, and object-recognizing algorithms - repeating the process every time the algorithms improve - to deduce more and more details about you as an individual? Well, we have that already, in services like Google Photos. And people flock to use such services, because they're "free".)
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