As someone who pays more attention to HBD than average, I thought this was quite enlightening in general ... I love the idea of being able to delegate HBD to other people from savings. You make a good point about taxation ... that could be an absolute bear, particularly here in the U.S. -- but this is the only major drawback I can see from "fiat world."
I add a thought to your thoughts; I think of HBD as a holder for Hive in nice USD denominations when I use it to give to people on Hive for various reasons. I don't have to think about "This person needs X number of Hive to get the USD value of Y that they need to convert to their currency and pay bills" -- HBD lets me know roughly how much that is, and since I earn here in HBD, I also can give USD-sized sums without going into my pocket. I have also paid for services connected with Hive with HBD as well, and delegation would also give that power to others. HBD also pairs with Bitcoin on Bittrex, and also @brianoflondon has the V4V app that allows exchange for HBD and BTC without an exchange -- so, in delegating HBD, we are giving delegatees a gateway to getting BTC. HBD is therefore only two steps from USD, but only one step from Bitcoin and its power everywhere crypto is available in the world.