Getting the shower pan hot mopped is a smokey smelly job, but it must be done. The tar acts as a barrier to water intrusion, which would otherwise rot out the wood framing and substrate in sort time. Even with backer board and tile, these lower extremities of the shower stall soak in water until it dries every day.
Without the hot mop tar layer daily use of a shower would shorten the life of this shower stall well before it's time. Considering the expense of bathroom remodeling, leaving out the hot mop is not a good option - no matter how smelly and smoky it gets.