It isn't a weird idea.
I used the concept to brood my chicks - hot water bottles instead of actual bricks because water has a higher heat index (aka specific heat capacity, thermal conductivity, whatever). It was also easier for me to heat water than to heat bricks. I used that in combination with a wool hen.
Once they are fully feathered, though, they can keep themselves warm. Feathers are extremely effective insulation.
It wouldn't hurt anything to put warmed bricks in a coop. It would be a much safer way than most other options people have talked about on chicken forums for people to feel better on cold days.
It would be a lot more weight than I would want to carry to get enough thermal mass to make much difference for more than a very short time.