Yup, I agree, that's a great point! Steemit, Inc. powers down to pay for salaries, so I don't see why that shouldn't be acceptable for merchants' case.

I also don't see most of these types of power downs with a negative connotation.

Merchants which need a lot of liquidity, should always keep some available, even if they powers up. They can also start using a service such as likwid if 100% liquidity is needed and if that will slow down or make unnecessary altogether a power down.