An important feature when dealing with DWI or fMRI data is the ability to split the 4D data, process each 3D data set separately, then recombine them into 4D.

There is a module to do the splitting called "Serialize volumes" (turning a volume collection into a serial list of volumes), and I have created a very artisanal "De-serialize volumes" module which collects a certain number of volumes and generates a single output. But it's not pretty, and it can fail very easily (it relies on copying all incoming volumes into a temporary directory until you have the correct number, then lets the layout move on).

It would be good to take those two modules and rework them so that the de-serialize part just waits for all its input files to appear and runs once (it is tricky for the layout tree structure, as it should stop all the serialized branches except one). Advice / help from anyone who understands the tree structure handling better than me would be great!