Making fuel an equipment that can be stored will defeat all the purpose of the game design. And it would be very lazy. We need fuel as an flow, the same as strategic resources.
It would be no difference between storing equipment to fuell the tanks and storing barrels. The only difference would be in the name description.
It depends on how much can be stored - if there was some kind of event that once your fuel stockpile hit above X, it was set to X, then that'd stop people over-producing. I'm pretty sure (and apologies to which mode it was, memory's shot - HPP or TRP maybe?) there was at least one HoI3 mod that dealt with it that way.
One of the good things a small stockpile (or just a soft cap) could do would be to model the ebb and flow of an assault - so there's not enough flow in the system for all of a nations planes, tanks and ships to operate all at once, but they can stockpile enough to give a couple of weeks/months where it's 'all in', but then it runs out and the offensive has to take a pause while stocks build back up again. If HoI was ever able to cope with supply-driven pauses in offensives, it'd be seven shades of awesome.
Will you be able to change the route supplies are taking? Ex Germany attacking Russia and sending supplies to the troops encircling Leningrad via the Baltic Sea rather than through occupied Soviet Lands to avoid partisans. Or attacking into Africa as UK or US and rather than depending on roads using your naval superiority to hop supplies to the next port.
What about transfer through allied territory or puppets?
Other questions that arise are the use of Supply Submarines.
I'm pretty sure we don't know the details, but it
looks like instead of supplies/equipment/whatever we call it flowing as per the old systems, the supply system is more like a network of interacting stacking limits, and if a unit is in an area where they're all under the supply limit (ie, stacking limit), it'll get replacement equipment instantly. So there's no need to worry about the route supplies take, but rather just making sure that there are enough routes and capacity so that the troops on the front are able to receive supplies.
I quite like the approach. The problem with doing flows is that to get an effective flow system to work, the player needs to tell the game what he's planning to do, so the supply system can prep itself as well (or the player has to do it manually, which would be micro hell) - or you get flows that start after a unit gets to its destination, which isn't how things actually happened - armies, for the most part, knew they'd be attacking and had supply arrangements in place to support the attack as best they could.
The downside is that it takes away one of the mechanisms that lead to pauses in offensives in HoI3, and at this stage I'm not sure what's going to replace it, but we'll see in good time.
