Re: 2012 Nexus models to stay at KitKat perrmanently?
I'm running 5.0.0 on a UK Nexus 4 with no problems. Chose to do a full install from scratch. New OS is great - with some fantastic features. Minor niggles - Photosheres will not play (they just error) and the promised integration with my Chromebook has not materialised - (may be a Chromebook issue though).
Couple it with Snapgragon's BatteryGuru and the batter life is very acceptable given it's two years old.
Love the open to application from notifications on lock screen, and the ability to not lock then connected to a trusted device - car BT or BT headset.
All in all a must have.