So my guess is we'll need to wait for HMTs to actually do any such experiments because a change there doesn't represent a change to the entire system and is therefore less likely to induce irrational fear.

But then be careful with your conclusions from the experiences made with HMTs: results from experimenting with HMTs wouldn't necessary correlate with future changes on the HIVE rewards system. As an example users might act more altruistic than normally in the HMT microcosms as they feel that anyway the value of HMTs would be too low to be worth it to be as greedy as usual. :)