So I've noticed a change in the behavior of Moto Assist now.
When driving, I'm connected to the Bluetooth in my Pathfinder. It's only Bluetooth calling, not media (2011 Pathy) so I can't play music, just make calls. With 4.4, text messages received when Assist was in driving mode were read over the phone's speaker. Now, they act like an incoming call. The display on my truck switches to phone mode, and the text is read over the truck speakers.
This actually makes listening and replying to texts much easier. I don't have to turn down the radio since the "call" interrupts any media playback, and the Bluetooth mic picks my spoken replies up better than the mic in the phone seems to (probably because the phone is in a vent mount and the air rushing past when the AC is on interferes with the mic).
Side note: I've seen no change in battery use...