I'd like to note I already use the IR sensor as a mesh and trigger'd zprobe at print start, but this is using a different set of tech that's collecting a lot more data, but used more coarsely.
Typically, TOF proximity sensors are for a course near/far detection in robotics, but there's some interesting work in applying these sensors for rapid plane geometry detection.
https://youtu.be/vJdfpmd6OE0
I can imagine you could poll a sensor like this across a bed at a distance to calculate a bed mesh at near distances or align it rapidly on print start, without the head needing to move across the surface to probe points.

There was a jetting printer that also collected lidar data every layer to improve quality, and a higher resolution TOF sensor could be used for arbitrary surface capture in QC of bridging or distortions as well.

@phaedrux I have dual lead screws (not independent) so unless I keep Z steppers on between prints, moving the bed or removing torque will tilt it between those two

@dc42 darn, looks like I'll have to do something like 4x4

I'm currently modifying my printing gcode for a 3x3 grid before printing (used to do a g32 5 point + a large occasional g29 20x20 point it adapts to, I'm finally taking the time to fully understand g29)

if I manually keep a grid of 20 x 20 for minor curves in my bed, then use a 3x3 grid each print, will the g29 printing gcode keep the 20x20 grid and be adjusted by the 3x3 grid or will the printer only print using the new grid?

I have already set up my g29 parameters for the 20 x 20 grid, so adjusting for a quick 2x2 or most likely a 3x3 after bed heating isn't an issue, it's mostly if the 20x20 grid can still be used, I don't want to spend an hour probing for each print, but the 20x20 grid allows for really nice first layers on a metal bed.

current bed leveling gcode,
; bed.g
; called to perform automatic bed compensation via G32

M561 ; clear any bed transform
M400 ; dummy for Z probe, stop any moves
G28 ; home all axes
; Probe the bed at 5 points (removed for now, only g29 is loaded)
; G30 P0 X26 Y3 H0 Z-99999
; G30 P1 X26 Y300 H0 Z-99999
; G30 P2 X263 Y300 H0 Z-99999
; G30 P3 X263 Y3 H0 Z-99999
; G30 P4 X144.5 Y155 H0 Z-99999 S5
M400 ; dummy for Z probe, stop any moves
G29 S1 ; load hight map (needs to switch to a csv file)
M376 H10 ;taper the compensation after 10mm

printing gcode needs to switch g32 for a g29 loading then 3x3 probing, and a macro for 20x20 probing to a csv needs to be copied/ made.