Good news.

I created simple silly "multiboot" which starts alternative OS after bootloader if user pressed VolUp (it's patched /sbin/preinit indeed). If user didn't press VolUp - Harmattan starts as usual.

USB networking start - ok
Starting android init process in chroot - ok.
adb (tcp over usb) working in android chroot -ok.

And phone restarts shortly after start because any process crashes, even staticly linked busybox. So my first clue is to blame aegis... I must investigate this weird behavior (nearest goal).
Update: only apps compiled using android toolchain crashes.

That's all atm. /me away to deep debugging session