Higher interest is likely to result in a large amount of HBD moving off exchanges, at least unless exchanges pay interest to customers, which they probably won't for HBD (due to it being too small to justify the effort on their part).

Right now there is no meaningful incentive to move your HBD off the exchange. But compare with HIVE where there is a lot on exchanges, but nowhere near 70%. That's because there actually is a reason to take your HIVE off the exchange and stake it.

True, any movement won't happen immediately so the first effect is a windfall to exchanges, but you have to start somewhere, in a chicken-and-egg fashion. You can't wait for people to move their HBD off exchanges to start paying interest, because they won't.