In addition to the comments already made here i will add that while I consistently see the dashed limit lines in cold temperatures before the battery pack comes up to nominal operating temps I DO NOT get the "battery is heating" warning, mentioned by the OP, when I have "range mode" selected. it appears as though, in range mode, the pack will just gradually heat itself using the normal heat from discharging the pack under normal driving conditions. As soon as I turn range mode off the HVAC system inside the car kicks into high gear and I'll get the "battery is heating" warning. So far, for me at least, this has been very consistent, even with the very low ambient temps we have been getting recently in the Chicago area. My guess is that even with range mode engaged there is a low threshold that would eventually trigger the battery heater to make sure the battery pack isn't damaged but I haven't found it yet, even with cold soaking the car at work for 4-6 hours in near 0 deg. F temps.
From everything else I've read on this forum it doesn't sound like this is typical behavior but I don't know if that is because most people are not driving in range mode all the time like I usually had been or because my car is acting differently for some unknown reason. It's only been recently with the truly frigid temps that I was prompted to switch out of range mode because it couldn't keep up and the car interior was getting less comfortable. How does everyone else use range mode in winter driving?