Lowering the power down time is honestly a trivial codebase change.. But would have to be something the top 20 witnesses have to sign up on.. In part I believe the power down time is so long in order to mitigate the potential for bad actors to buy up HIVE, do disruptive things and then be able to quickly power down essentially costing them little to nothing in terms of cost of attack or time.

It's a deterrent.. However it acts both ways as well as you've mentioned above.