20% is sustainable if the growth rate of HIVE is much higher.
This is the key point. If 20% on HBD turns out to be sustainable, you end up wishing you kept the game reward fund in HIVE. If HIVE tanks, bad luck, nothing you could do.
While transacting with HBD is the obvious thing to do and helpful for the game and the blockchain, putting the assets in the HBD savings is a loss-loss proposition.
Basically, as a HIVE proponent, you want to persuade every one else to buy and hold HBD and avoid that strategy yourself. So yes, you want other projects to follow the idea - but only those you are not invested in.