In addition to the points about tires, tubeless, rims, weight ... Not all snow is created equal, light fluffy pow is ridable when much deeper than heavy wet snow.
With all that said, I'm able to ride 4 inch deep snow consistently and can ride deep snow depending on the condition of the snow.
One last consideration, is the riders strength and bike handling, snow conditions that are ridable for a strong/experience rider will be unridable for a n00bie.