I don't know how the internals of the keyboard work, but by doing monkey-testing I'm now pretty sure that the problem I have with the XPS inserting multiple spaces frequently is a mechanical one.
Testcase: Press space and any letter of your choice in quick succession. For example just type
d d d d d d d d d d......
Don't use your usual typing position, but just use your index fingers for both keys. Now while you're typing those alternating keys, notice that when you move to the edge of the spacebar (left and right end, and also vary the point towards the screen and towards the touchpad), the double-space problem occurs, while it never occurs when pressing it in the center, no matter how fast you type (and the alternating between regular letter and space is only to see the double-spaces).
As I have my thumbs below the "m" and "c" and thus hit the spacebar at the corners, I'm prone to triggering the problem frequently.
Please comment whether you confirm those observations (no double-space when using center of spacebar, double-spaces when using the edge of the spacebar) or not.
(German Keyboard layout on XPS 13, FullHD, i5)
I have exactly the same experience.
Had a lot of problems with duplicate keys out of the box. Installing the latest BIOS fixed it for all keys but the space bar. After investigating, I noticed that the spacebar's resistance feels quite different and unstable on the edges vs. in the center. And indeed, the more I hit it at the edges, the more problems.
This probably explains why some people aren't affected at all. Depending on your typing style and hand size you might never hit the spacebar in a problem area.
I had to send my XPS13 back, because this made it impossible to use for programming. Since it's a hardware problem I don't dare to buy another one, which is too bad because I loved almost every other aspect of it. (Everything but the Broadcom wifi adapter, which is just a very silly thing to include on a developer edition/linux laptop).