With the addition of new harvestable currencies I personally would like to see new nodes available as guild hall upgrades that act as a tertiary way to get the new currencies. Just off the top of my head you could make a number of upgrades, a first set based around which currencies you harvest, and then a second set of upgrades on the number of harvest tries you have.
Also it would be good to see these currencies implemented as very rare drops from the wvw nodes. Possibly with an associated wvw mastery.
Thoughts?