I've considered bringing significant outside capital into HBD many times as this is sustainable for the time being, but I am so very risk averse, as those funds are currently offsetting interest in my mortgage.
As one of the top 500 earners in your list, this is a great way to sit and earn something "safely", that will, at some point; likely return to the HIVE eco system in some way or another. (Be that Splinterlands, or a return to HIVE Power and manual curation)
The ramp "out" is the difficult thing (risk wise) as while the market is highly liquid, the minor fluctuations in HBD's price make it unattractive to dump everything I own into HBD and to supplement my other income.
Having said all that, I've been really happy with the returns.
I have also considered converting significant amount of USD from traditional savings funds to HBD. While HBD is low risk, there is still some unknowns we may not have considered to go all in. But there are also risks in traditional funds as well. So, I wouldn't mind converting them to HBD. My concern is 20% APR is not permanent, and it can be discontinued or lowered at any time by top witnesses. For this reason, I haven't decided to go through all the trouble of moving funds.
The second reason I would be hesitant to do something like this is, because I would probably end up buying more bitcoin instead. While HBD is great as a stable passive income, there are higher rewards in bitcoin over time.
For these reasons, I will probably keep things diversified and have a little bit of everything. lol.
Don't put all your apples in the same basket, or something like that. :)