We have the same challenge, except that in our case the issue is hardware. Hardware comes at a very fixed iteration speed, usually around 3 months for somethin

We have the same challenge, except that in our case the issue is hardware. Hardware comes at a very fixed iteration speed, usually around 3 months for something of moderate complexity. That's how long it's going to take to do schematic capture, layout, pcb manufacture, board population and bringup. Even if you can speed up this iteration process, there is still a sizeable financial cost of going around the loop. This means that at a project level you need to do a certain amount of requirements capture before you start work on electronics. You can then run your software in a fairly agile manner 'inside' the project, hoping that the inevitable changes in requirements can be dealt with in software. Obviously you design your system in such a way as to increase that likelihood.