Since it's been confirmed that the device will accept 2280 m.2 drives, I figured I could upgrade my device after purchase rather than paying a premium for more storage direct from Microsoft.
The two rubber feet on the bottom are resilient and non-stretchy; compared to an HP Envy 15 I've upgraded the ram on in the past, if you're careful the surface's rubber feet won't detach from the adhesive and will easily slot back into place. They lift up relatively easily from the ends with a fingernail. Underneath the rubber foot towards the lid hinge are 3 torx T3 screws, with 4 more of them under the bottom rubber foot towards the trackpad.
After removing the screws, pulling the staggered bottom base from the rest of the chassis on the corners near the hinge has some give, but there is the sound of adhesive being pulled up with this. I attempted to use a pick to slide underneath and continue going around, but there doesn't seem to be much give here. At the bottom of the device near the trackpad seems to be a divot in the adhered trim that wraps the bottom of the device between the vented base and the keyboard deck. It seems like this trim is the main barrier to getting into the device and is almost certainly there to facilitate the wireless charging for the pen.
I'm going to hold off on any further disassembly until I can find Microsoft documentation or another user that is willing to peel back the adhesive or find another way to remove the bottom portion of the unit. The keyboard deck does not seem to lift up at all either when the screws are removed.
EDIT:
So I followed itsage's guide to remove the adhesive and the last two screws, and it worked! I was able to get into the device (after unplugging the battery ribbon cable). There's also a few thermal pads on the inside of the bottom frame for heat dissipation of the nvme drive with the surface area of the bottom of the device.
Be warned about the power ribbon cable: it was a pain to plug back in and my anxiety of handling such an expensive device combined with shaky hands meant I accidentally broke off a slight bit of plastic on one end. It should clip in without much issue if you are patient.
Here are some benchmarks of each drive: