At long last, Marshmallow has arrived for me on my Sony BRAVIA KD 43X8305C in the UK.
It... Immediately broke Netflix.
Had to uninstall the app, clear data/cache, reinstall (update), and sign in again. Now it seems fine. The misses was not amused, neither was I.
On the plus side, a Bluetooth keyboard that didn't work before does now, so that's a bonus. Sadly can't seem to pair with Sony Bluetooth headphones though, which I thought was something that was coming with Marshmallow, and was the main thing I was looking forward to. Bummer.
Yeah, so, Sony have done a piss poor job of this. YouTube also completely broken. Trying the same things as I did with Netflix didn't help.
Now trying a full factory reset of the whole TV.
Thanks Sony. You slow, incompetent arseholes.