Gorgeous. But two concerns on practicality...
1. It looks like switching the gas setting would require removing the barrel at least partway. Not a show-stopper, but a show-slower so to speak...
2. The weight at the forend. I've not fired an XCR-L, but I have fired the XCR-M both with the keymod+light barrel, and the quad rail+heavy barrel. While the keymod and light barrel is an improvement, additional weight at the front of the rifle is a step in the wrong direction.
What this would be PERFECT for is a 20" heavy barrel XCR-M, and set that summ##### up as a Designated Marksman's Rifle - a pistol grip with a palm-shelf, bipod, and a high-end, high-mag optic, and a different stock (the FAST is a bit too wobbly for a decent DMR, and a monopod at the back would be a solid choice too).