This is more of a fun experiment than a serious venture into crypto mining. Well, at least he's clear about setting it up "to annoy gamers."
You have to consider that this could be another door of opportunity to upgrade the way we mine bitcoin, I am not interested in the part about annoying gamers. This could be a possible start up for aesthetically pleasing mining rigs.
As regards cost-benefit, I'm not sure if it's practical for anybody to do this. The car has a battery which could support the mining, of course, but then for the battery to charge, the alternator has to be working. Otherwise, the car's battery could easily be drained. For the alternator to work, the car's engine has to be turned on, thereby consuming fuel.
We need to run the numbers on this one to see whether the cost in fuel is better than having the rig stationary at home. I don't think that it is a practical especially the car is priced at around 150k USD, but if we were to see past that, and try it on a cheaper economy cars, I think that it has some potential although the cooling will be the big problem and protection from the elements.
This is, therefore, practical only when Simon's on the move.
If the rig could be reduced to a smaller scale and the issue of heat and cooling is resolved, I think it will be more practical although the mining output will be much lower.