I'm thinking that would change hardness by temp. That too, could be interesting, if you got it *just right*, as it would initially hold a person's weight, but as it took heat, it would soften, so the person would start sinking. You'd need some reason for the sinker not to move. The deeper they do sink, the more body contact to give heat to the wax, so the faster it gets soft. (this will likely give a female model cold feet, which usually isn't a happy thing, but it would also likely give her goosebumps and erect nipples, both of which are major happy things in my humble opinion!)
I'm thinking (if this mix was found) that this would be the perfect deathtrap to leave some costumed "superheros" in for some sinister scientist badguy. If it were slow enough, the heroes might not even realize what trouble they were in. Focusing on getting ropes untied (or picking the lock of some non-standard handcuffs, or whatever) could keep them distracted until they were up to mid calf or knees, then the real fun starts!

Then again, maybe the mix is not soft enough to trap a footstep until it's bath-temp, so a heated pit would be needed, and the pit could be cooled to make it as hard as the floor.
Fun idea!