I like UNPHAT idea, as long as it is executed in an agile way. That is, at a given moment, perform multiple stages that can be done safely without feeling block

I like UNPHAT idea, as long as it is executed in an agile way. That is, at a given moment, perform multiple stages that can be done safely without feeling blocked by other stages, then iterate, where in each iteration, one tries to do all possible stages better. For example, after reading papers, don't consider previous stages "DONE", and revisit understanding the problem based on the new understanding, and so on.