I see the Form 2553 instruction's last update was stamped 2020.  The reasonable cause under Rev. Proc 2013-30 does not require a Form 1120S to be filed as it is a Regulatory Election for a qualified corporation.  I found the below guidance (as of January 2021) helpful (see page 15): 

https://www.irs.gov/pub/irs-irbs/irb21-01.pdf

.02 In lieu of requesting a letter ruling under this revenue procedure, a taxpayer may obtain
relief for certain late S corporation and related elections by following the procedure in Rev. Proc.
2013-30, 2013-36 I.R.B. 173. This procedure is in lieu of the letter ruling process and does not
require payment of any user fee. See section 3.01 of Rev. Proc. 2013-30, and section 15.03(3) of
this revenue procedure.

My understanding is that under this guidance, only when the requests were denied by the IRS, we can proceed to the private ruling.  But up to now, we have not experienced any denials yet under Rev. Proc 2013-30 as it is a regulatory election, I believe.