Not exactly on all Treble devices. In fact I have two phones that can only boot one of his sGSI roms. A/B is a mess when it comes to these roms. And his roms also need bigger system partition than what we have (not a problem anymore as we have EPR). But yeah, init, selinux etc, basically mess when it comes to booting anything on this phone or A/B in general. I was hoping that Android 10 would make stuff easier but nope. It's even worse now. Now on top of init and selinux we also have Apex and Codec2 lol.
Yeah but for this reasons you should flash also zygoyte_fix and permissiver (kinda selinux fixer)