When you say it works perfectly, what do you mean? Does it read a text without any intervention? Mine puts up some kind of screen asking me to say "listen now", which is totally defeats the purpose of a drive mode. I did look at the thread you linked. There is NO doubt that this drive assist is an issue with the Moto X. Hopefully they fix it with some kind of update....
Sorry for not answering sooner. When I say it works perfectly on my phone, I'm saying it's working as designed to. Maybe not "perfectly" depending on one's personal needs, but "perfectly" as it's designed. It's been a while since I got a text while driving, so my memory might not be totally accurate, but every interaction with a text or phone call is by voice; I don't need to look at or touch a screen. It lets me know who is calling and texting by voice; it reads me the text and asks me if I want to send a pre-written reply (which I believe can be edited in the Assist setup); it asks me if I wish to answer or ignore the phone call; if I answer the call, it goes automatically to speaker phone so I don't have to touch or mess with the phone at all. To me this maximizes safety and convenience and is "perfect" functionality, and it has worked as advertised from the get-go on my phone. Not saying others aren't having problems, but I didn't.
One thing that I think is excellent and critical to the overall "safety" aspect is that the driving mode activates automatically. I therefore never get into a situation where I'm distracted by a phone ringing or a text notificaiton and tempted to answer/look at it. Or, the sort of situation where I think of the Driving mode after I've started driving, so I'd be tempted to grab the phone and go through the process of activiting it. It's easy enough to disable if I'm in a car as a passenger (right up top in the pull down notifications screen).
I did have problems with the "resume music" setting. I believe it's intended to only come into play if you're listening to music when it (the music) is interrupted by the Assist notifying you of a call or text, and then resume the music when the interaction is done. On my phone, as soon as it detected I was driving, it would start playing music, and the song it played didn't have anything to do with any pattern I could detect. I disabled that feature, but haven't tried for about 3 weeks, so it might have been corrected in an update.
I like the "sleep" feature too, but haven't used the "meeting" feature at all.