The preamble to the Section 199A final regs gives the option of using the proposed regs for 2018 tax returns (all final or all proposed, no cherry-picking).  The proposed regs did not contain the provisions about reducing QBI by one-half of SE tax, SE health insurance, and SE retirement plan contribtions.  Ror 2018 returns, is it legitimate to use the proposed regs and not make those reductions to QBI?