I would expect the 20% to be tapered back eventually
Yes I don't think anyone would suggest it be "permanent"
It is very important to make clear at all times that witness-set APR is variable and can change at any time. When the cost of interest exceeds the value of promoting the chain (either because the former is too high or the latter too low or seen as diminishing returns) I would expect it to be reduced.
If or when longer term bonding / locking system is built, one of its great features will be a guaranteed APR, rather than an APR that can vary based on witness signalling. If that can be built before the APR on the 3 day lock in gets reduced (for whatever reason) it will be quite a classy move. Will certainly put us ahead of other chains in this feild who have ultimately had to reduce their APR eventually. I think with the low market cap of hive and incredibly low market cap of hbd or usdh or whatever we end up calling it, the potential for this to outperform where others have failed is tremendous.