Can a "proper" Linux userspace run on an Android kernel?

I've been reading about the challenges of getting Android phones to boot up using a close to mainline Linux kernel, and it got me thinking, manufacturers have their own kernels with all the correct drivers, and Android ROMs like LineageOS use these kernels with great success on many devices (of course it's not 100% there due to SafetyNet, etc. but the majority of features work). So my question is: is it possible to use these kernels to boot a conventional Linux userspace by having them start up something like systemd instead of Android's init? If not, what prevents that?