I had the upgrade installed in my 2014 Model S last December (2015). Highly recommended! Speed of map updates is improved, especially in weak signal areas. Overall coverage is notably better as well.
Seems like we've been asking for this for quite a while - now Verizon has announced and even faster service called XLTE. It's the latest advancement of Verizon's 4G LTE network: double the 4G LTE bandwidth.
Agree...a car this progressive should not be 3 years old in its offerings for connectivity. I would think a lot of us use Android phones and have 4G/LTE connectivity. If we could get that on the Model S, it would be appropriate and way past time!