That would be my ideal configuration. It's strange that MS is targeting businesses for the SP3 but delays LTE capability. Even the SP2 until now still doesn't have integrated LTE. I have cellphone service with Tmobile, so we get 1 GB/month free of tablet LTE free until end of 2014 and then 200 MB/month afterward. Not a bad deal since I can still tether with my cell phone.
Yeah, its is strange but I think they main two reasons are
1. Intel. They still don't have a core chip with built in LTE radio. Putting a separate LTE chip would increase battery consumption and add an extra component to the motherboard, it would also require separate drivers, etc.
Broadwell doesn't look like it will have built in radio as well, but it might play nicer with 3rd party chips.. the Asus 300 Chi has an LTE option, which is promising.
2. Design. Having an all metal casing would block the LTE signal to the device too much. Its not exactly as bad as smartphones where you have a very tiny screen, which could be used as an outlet, but still.. having only parts of the screen side open to LTE radio waves is not ideal.
To integrate the current gen antenna properly you need plastic, which is what they did on the Surface 2 LTE
There is a plastic bar at the top of the device
The same would need to happen to the Surface 3 pro
Now, since they got Nokia's tablet designs, they are all about radio connectivity and antenna placement. Their work on the metal Nokia N8 was outstanding.. pretty much everyone copied the antenna design from that. So maybe they can take a closer look at their stuff and see what they can do.
Or maybe just go full high quality plastic and be done with it.
The Asus 300 chi which I mentioned is a question mark for now. The unit they had on display was all metal, but we don't know if that particular one had LTE radio built in.