Making void dust stackable is a nice idea, but the exchange rate for CP/ISP/AN cannot be justified in today's economy. You would never farm campaign to trade AN for void dust to sell. From the opposite perspective, you would never pay more than say 20k per void dust to do VW. The exchange rate would have to be much more favorable than it is now in order for void dust to even be considered as a possible solution for this.

In reality, the core of the issue is that voidstone generation has to be improved. The generation of items and gear can only be justified because individual fights are very quick. It is generally accepted that when you join a group, you will be participating in 6 fights. Even under the best of circumstances, this is 3 days worth of voidstones. The only reason people are able to do VW is because the event was dead for quite some time and people were able to amass great quantities of voidstones that way. 4-hour regeneration is not unreasonable.