I have a Surface Pro 3, and while I really love it for mobile processing, I'm not sure I would love it quite as much if it was my only machine for editing. I also have a nice desktop with significant storage space in a RAID 1 array for redundancy.
-powerful for its size
-pen/screen combo makes for quick and easy masking, selection, spot removal, etc.
-screen size (resolution is good, but the actual screen real estate is lacking)
-limited horsepower compared to desktop
In fairness, all of the cons will be cons for any laptop. I do think the Surface is probably one of the better choices for mobile photo processing, and I can't say enough about the pen and touchscreen combo. How I use it is likely going to be different than what you're hoping for though. For the most part, I'm using it to import photos, very selectively cull (thanks to the limited SSD space), keywording, and basic processing (spot/backscatter removal, contrast adjustment, sharpening). My camera's white balance is set to my strobe temperature, so I'm not generally making color adjustments on the laptop. That said, perfect color calibration isn't super important to me (on the laptop) and anything I'd print would go through my calibrated desktop. It's a difficult machine to calibrate perfectly as mentioned above, because the brightness control does not allow fine control whatsoever. You can choose 0%, 25%, 50%, 75%, 100%. "Battery Saver" mode dims the screen a bit as well. You also mentioned the lack of consistent ambient light, which is an issue, but again, would be an issue on any laptop that's being moved around. When home, I move the images onto my desktop storage, merge the catalogs, create the necessary backups, then delete files off the laptop to make room for the next trip.
The screen-size of the Surface is definitely limiting, especially if you keep any of the Lightroom windows open. It's simply difficult to see the image and I find myself flipping between "D" and "F" quite a bit to get a better look at what's going on. It's not a deal-breaker, but it's nothing like editing on a proper, large desktop monitor. You can also use Lightroom on a Surface in "tablet mode" which allows you to minimize the amount of space Lightroom is using for it's various menus. It takes some getting used to, and I still very much prefer the normal mode, but I'm trying. My wife has a pretty modern Macbook Air that I tried out with Lightroom in the past, and for me, the screen size difference was negligible. They're both pretty small.
Hope that helps!