[2022] A question about heatmap and zombie spawns.

Indeed. The only direct effect of the ‘heat’ will be to spawn screamer(s), and they won’t be any better equipped to spawn or reach you than other, regular zombies.

Water will be changing in A21, so hopefully the zombies will be better able to handle this case.

Here’s what’s known publicly.

Water Simulation
All new water coding--water is no longer a block but a water voxel
Water voxels flow into neighboring voxels that are marked to allow it.
Water can be in the same space as a block
Water does not flow or fall continuously like a river or a waterfall
more details to come.

The fact that water can coexist with blocks is encouraging. It suggests that zombies may be able to spawn and do pathing calculations on the underlying blocks.