I think incentives drive behavior and it really depends on which type of crowd you want to attract. Having a long power down period will likely attract longer-term users/investors. On the other hand, reducing the power down period will invite more short-term speculators.

The ideal scenario will be to have a few lock-up options with different duration. Of course the longer you lock-up the higher the ROI. Loom Network is one such crypto project which is doing this.