I have tested in tribble for 2 weeks now and I like the doff system, it really adds a another dimension and gives us something to work for.
However after getting to tier 3 on diplo I started thinking about the doff system in combination with my fully developed VA/ambassador chars on holodeck.
It would mean that doff diplomatic missions would be kinda pointless from the start and that would really be a shame.
So here is my suggestion:
Give the diplo XP the same range as the other doff mission categories.
Change the current diplo tiers with its rewards to acolades so the bonuses like transwarp can be gottten that way in a range of for example 1000, 2500, 5000 and 10000 DXP with ofcourse the rewards in the DXP skill tree doing the same math as the other doff skill trees.
This way we vets can still do the doff diplo missions in holodeck and work towards the doff rewards without disrupting the current diplo rewards.
And as a last suggestion maybe for the future, make it possible for main chars to earn points in the different catagories by doing missions related to that category, some explore missions could easily be used for that like the scanning missions could earn science XP, helping a colony getting rid of roaming borg colonial xp etc etc.
Just some thoughts, hope it makes sense to a dev out there