I really don't understand why MG keeps these updates a secret.
When I got my Kia Stonic two years ago, the software had a few bugs. They eventually released the upgrade to the public, and yes, some users bricked their units. Some users couldn't update, some times there more more bugs introduced than resolved.
But when all of this was going on, the user community, through the KIA forum, managed to get KIA to fix the bugs, have a somewhat direct line with support, and low and behold, 6 months later it was near bug free, and this wasn't just one model, this was on their entire product range.
That's why this "better the dealer does it" attitude is just not sustainable in a world where bugs are just what they are and given the customer base, no amount of testing by the dev team will ever fix it.
And even if they made it available to the public (like KIA did), do you really think they are going to have more problems than they can fix? More like the opposite: early "canary" testing and adopters is exactly what gets things fixed.
As for whether an upgrade could cause death or injury: what we are talking about here is the infotainment system. Not the frigging ECU.