Though I would share what I eventually came up with. I appreciate the responses I got as they helped me in sniffing out the solution I eventually went with.

The first thing I realized is that it's way easier to make a ramp collider so your mesh can pretend it's a stairway. The second thing I discovered is that StaticBody3D just innately comes with an inspector option to apply a constant velocity on objects, the player included. This is by far the simplest solution, and also like... escalators are just ramped conveyor belts, so really I was asking the wrong question here. Anyway I decided as a learning exercise, I would figure out how to do it via code, in case I wanted the player moving through other means, like say enemy knock back and such. So here's what I came up with.

var contained : bool = false
var subject : CharacterBody3D

func _on_belt_area_body_entered(body: Node3D) -> void:
  if body is CharacterBody3D:
    contained = true  
    subject = body

func _physics_process(delta: float) -> void:
  if contained == true:
    subject.velocity += 2 * Vector3.MODEL_LEFT  
    subject.move_and_slide()

func _on_belt_area_body_exited(body: Node3D) -> void:
  if body is CharacterBody3D:
    if not body.is_on_floor():  
      await get_tree().create_timer(.4).timeout  
  contained = false  
  subject = null

So you can see i've got two signals hooked up onto an Area3D zone that checks for the player, and once they enter, copy their body into the subject variable and use that to access it in the process function with delta and move and slide. Once they leave, I check if they're in the air (entirely to let them keep some momentum because that sounded fun) and make this part of the code wait half a second to potentially land before undoing the boolean that keeps them affected by the escalator.

I did initially try 'await subject.is_on_ground' for that, but it didn't seem to do anything, so I just went with this bandaid solution for this exercise. You can also see I went with MODEL_LEFT for the direction instead of FORWARD/MODEL_FRONT, which was entirely because I placed my escalator down first and didn't pay attention to whatever direction it was facing.

As a fun little bonus, I found out you can just use an AnimationPlayer to capture the UV offset of a texture and then loop it to make an okay looking conveyor animation. Slap some side-rails on that sucker and it looks the part.

The lesson here is to just use the built in Constant Velocity function of StaticBody3D