Yea my guy already has about 50 pounds on your puppy, and he is only 14 months old90 lb German Shepherd in 23 XP, fits... just barely. I wouldn't say he's wild about the 6 seater configuration.
Am trying to get into tesla the same time that the manager of the service department for my dealership is in (may travel to a larger location to ask as well)
Right now I have removed the rear seats of my model 3 performance and have bought a twin memory foam mattress topper to cut into the exact shape of the exposed lower seat area. Placing a waterproof (stitching it) over the memory foam before placing it in the car for good then will look at a different fabrics to place over for a pleasant look that will flow into the lower carpet area (something easy to clean ) untill I get a solid answer and prepare for my purchase
This extra clearance for height works well for now (barely xD) while maintaining the seat belt lower locks to plug in his harness still for saftey and not expose him to direct metal surfaces or small opening (where his paw/toes could get stuck)
I can provide images if you guys like as things progress on this and the model X inquiry