This is already possible. You need to create an .SQF for the custom loadouts. Including all of the possible items.

edited to clarify - i'm interested in an in-game solution to this. i kinda guessed that with some extra files you could perhaps do it, but an in-game solution would still be preferable and, i would imagine, vastly quicker

I'm not sure about this suggestion. Obviously I'm not a dev, but I imagine they need to draw the line between adding tools mission designers can utilize in a widespread fashion and tools mission designers should create for themselves on an individual basis.

You're asking for a feature that would be quite complex to implement which can be very easily scripted by a mission designer (in a much more flexible fashion that offers more control too).

Although, just to clarify: Are we talking about exporting the loadouts from the VA or using the Arsenal module? Or both?

i don't see how it would be awfully complex for BI, as drakeziel mentioned, it's apparently already possible using SQF.

I am talking about the arsenal module though yes, for use in Zeus (which is where i don't think the .sqf solution would work, assuming the .sqf goes in a mission folder or similar)

It wouldn't be overly complex, but fairly complex relative to the result it'd produce. The most complex parts would be:

1. Displaying the system intuitively to users via the interface (documentation aside as I know first hand not everybody will read that).

2. Figuring out how best to handle magazines/items that can be stacked within such a system.

3. The process of integrating said new system into the existing one. I haven't looked at the module specifically yet - if it's passing a unique argument to the VA function then this wouldn't be too hard, but if it's using an existing argument and you want the new system to work for that argument you also need to think about instances of the VA outside of the module.