the only way to attach such an election would be to paper file your return.
having worked for a professional tax prep firm, not once did it attach such an election though I would agree that the Rev Proc in the notice requires it IF YOU WANT THE BENEFITS OF SAFE .
the firm's reason was that no one kept contemporaneous records for 2018 to factually determine that the required 250 hours was met (such a requirement is in effect for tax year 2019). Note that not all hours spent by taxpayer count but hours spent by gardener or plumber would so basically TP would be signing under penalties of perjury that they met the requirement when in fact they might not have anyway of knowing for sure or proving it. also notice that if the SH election is not claim other methods can be used to demonstrate that the rental activity is indeed a trade or business.
