A big downside of that proposal is that everything takes up much more space, which makes it much harder to keep track of what else is going on. In toy problems

A big downside of that proposal is that everything takes up much more space, which makes it much harder to keep track of what else is going on. In toy problems it is fine, but in real problems having the answer to "did the code already check for i == j" visible at the same is really important. Let alone context such as "is this the reference implementation for single core validation or the vectorized function" or "is the radius at timestep n or n+1/2".