Seconding this. I'm currently working on a large texture sheet that I want to edit seamlessly but need to save it in multiple slices for shader and texture size limit reasons.
My current workaround is to create the slices as separate .tif files with a linked smart object back to my large PSD. I reposition the smart object in each "slice" document to show the cropped area I want. When I save the PSD, I then tab over to the slice documents (wait for smart objects to be updated first), then save each in turn.
This works well enough, but I would rather just be able to export my slices to .tifs in one go and without waiting for smart objects to be updated, which takes some time with my large PSD.
Another downside of this method is that alpha channels are not available over the smart objects, so I must put the PSD's alpha channel in RGB space, save, switch to slice documents, and then copy RGB to alpha.
Some way of generalizing slices to more than just web and including support for alpha channels would be much appreciated.