The way I understand it is this:
Storage blocks will have just as many slots as they have now, but there will be stack caps in place (say 5k per stack as an example, we don't know what the numbers will be).
Storage for things under that amount per stack will function exactly as they do now.
You can also put down cargo blocks that are like area sensor blocks in that they are invisible when you're not in build mode, and slave them to a storage box. The storage box will then act as the interface to the cargo blocks, basically letting you bypass the stack limits.
So lets say the stack limit is 5k and you want to store 10k salvage modules. You could either store two slots of 5k each in a storage box, or you could link some cargo space to the box and then it would show up as you having 10k in one slot, with it actually broken up into pieces over in the cargo area. They've also said the cargo block limits will be higher than the storage box limits, so that you have incentive to actually use it.
All of the sorting and automated pulls your storage boxes do now will be maintained, and they will work in the same way, they'll just be using the cargo area as extra linked storage space.
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Another way to look at it with today's blocks, lets say you have a master in box, and that stack caps are in place. You then have a storage box linked to it that pulls nothing but salvage modules. You then have 9 other boxes that do nothing but pull all from that first one. You now have 10 storage boxes that auto-fill themselves with salvage modules.
Now have an 11th storage box that pulls all from all of those 10 other boxes so that its constantly full of salvage modules for as long as you have them.
Thats kind of like how storage boxes and cargo will work. That one box at the end "pulls" everything from it's linked cargo, while at the same time being the inbox that pushes stuff back into the cargo space as well.
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Or at least that is my understanding of it at this time.
