Thank you for your kind words 
the navmesh object is an internal (internal to recastjs) representation that has no meaning for babylonjs.
But, you can get a triangulated mesh ready for rendering this way:
navmeshdebug = navigationPlugin.createDebugNavMesh(scene);
var matdebug = new BABYLON.StandardMaterial('matdebug', scene);
matdebug.diffuseColor = new BABYLON.Color3(0.1, 0.2, 1);
matdebug.alpha = 0.2;
navmeshdebug.material = matdebug;
I guess you can use this mesh for XR.
Glad it has been useful! 
and happy that you’re extending this to XR, I might go there soon :P. What app are you building, if that’s public yet?
Hi @tibotiber, we are plotting a potential rebuild of framevr.io on babylon. This would be a very, very big deal for us, so just doing some initial exploration and prototyping. (and in case interested, @Cedric, some people from our team chatted with Jason and Ranaan on your side last week. was a great meeting).
FrameVR looks really cool. Gave it a follow on Twitter, thanks for sharing.