What fraction of users do you think have a legitimate need to sideload apps on Android? I would imagine it's much less than 0.5%. Developers and technically-minded power users must be a tiny minority amongst Android users given that it has an install base in the billions.
Right now, not many. My point is that they aren't flipping a giant switch from an open platform to a closed platform. They're boiling the frog -- slowly removing features until all choice is gone.
A few more years in this direction and Android can be as locked down as iPhone before Apple was forced to allow sideloading
