Also, myriads core business is automotive and embedded devices.
So from market pov, alien dalvik for mobile phones is only a side project for them since many years. Explaining maybe why they are not so keen to "upgrade" to newer engine than kitkat unless paid for by a demanding customer?
Making the importance of supporting Anbox within this community even more important btw.

On Topic sony and bootloader.
They kind of invite you to unlock to participate in "sony open device program" because "Openness is important to Sony" but do not make an exception of any kind when it comes to warranty. the website explicitly states:
worstcase: At least the Xperia X is a common model and can be repaired in independent shops which is a step forward from Jollas own hardware.
bestcase: Special sony/jolla agreement that flashing tested sfos image somehow is covered by special warranty agreement, maybe if done with jollas rumored own user friendly flashtool?