My TV is up and running again.
Be warned, these Bravia TVs suffer from the same issues as old Samsungs, similar to sudden death.
My TV had 5 years, I only use it for Youtube, Kodi... Storage was always empty (I use a NFS disk for media), yet it took the same path as many others.
When your TV starts randomly freezing, and hard reset doesn't help or actually makes it worse causing a bootloop, it's a bad eMMC signal.
eMMC can be changed, but the RPMB area stores some keys, you can't read it without a secure key, so that part will be lost.
After cloning the memory to a new one, the TV will work again, but Sat TV, Netflix, ChromeCast won't work due the missing DRM data.
Anyways, this TV hardware was becoming old, it's been a while thinking on adding a TV box.
The lastest Chromecast (with Google TV) came just in time, the remote controller should rule everything, as the chromecast is able to control the Tv using HDMI CEC.
So I don't recommend modifying them. As far as I know, there's no easy way to reinstall the firmware.
Sure, you can force the update by pressing PWR + VOL- then inserting the power, it will copy the update... then exit at ~50% because it will check the version, and if same or older, it'll skip it.
So if you modify something in the system, unless a new way to reinstall comes up, you'll be pretty much screwed up. That, or make a backup of the eMMC first, which isn't for everyone, requires soldering, etc....