One question is whether SP are in mandatory escrow (i.e. not the escrow agent of the recipient) and thus the SP would not taxable until the minimum (i.e. 6.5 weeks weighted average) time it would require to power them down:

http://www2.econ.iastate.edu/faculty/harl/ald/HarlAgLaw20110218.pdf

However it appears the escrow must actually benefit the payer (i.e. escrow protects against non-performance of the recipient) or be forfeitable in order for the deferral of taxation to apply:

https://steemit.com/steem/@cryptotax/are-steemit-rewards-taxable-in-the-usa-part-2

Certainly any delay added before powering down is certainly not a valid deferral of taxation because the said delay is controlled by the recipient.