No they won't. Facebook is in the Play Store on Android, and they used the Windows 10 Store up until they abandoned their desktop client. They want the largest user-base possible, which means they want finding and installing their app to be as frictionless as possible.
No mention of sideloading in that link, instead it mentions a Play Store and an App Store listing. It's almost as if there is a lot of dangerous crap in those stores as well...
I have conflicted feelings about "Facebook Research", but where I always end up is this: if citizens of a free society want to give away their data in exchange for a couple extra dollars a month, they should have that ability in a free society. People can and should be educated of the risks so they can make informed decisions, but trying to stop it is ultimately a fruitless errand (Even as Facebook is a pile a scum, don't misunderstand me.)
And it's all somewhat beside the point, isn't it? Facebook Research was usable on iOS. By the time Apple put an end to it, the backlash had become so significant that Facebook pulled the program from Android anyway.
