Disclaimer: I am not a tax professional, IRS employee, lawyer or anyone with authority to provide interpretation or suggestion of how the CARES Act $100k retirement distribution will be handled as far as taxes are concerned. I'm merely a woman who likes to research, had a similar question and went in search of an "answer." I encourage you to speak with your own professional advisors.
See Q7 and the related referenced Notice 2005-92
https://www.irs.gov/newsroom/coronavirus-related-relief-for-retirement-plans-and-iras-questions-and-answersIn theory, if the IRS publishes the similar guideline that they did for Katrina (as their FAQ would suggest.) It appears that in theory, someone who qualifies for a penalty-free distribution under the Cares Act, could have use of the funds until their 2020 extension period (Oct 15 for most people) and not have it affect one's income. Even if one doesn't file an extension, it appears as though one could have use of the funds without including it in income as long as they repay it before they file their taxes.
https://www.irs.gov/pub/irs-drop/n-05-92.pdfPage 11, 4D
If a qualified individual includes a Katrina distribution in gross income in the year of the distribution and recontributes the distribution to an eligible retirement plan after the timely filing of the individual’s tax return for the year of the distribution (i.e., after the due date, including extensions), the individual will need to file an amended tax return. The qualified individual will need to file a revised Form 8915 with his or her amended return to report the amount of the recontribution and should reduce his or her gross income by the amount of the recontribution, but not to exceed the amount of the Katrina distribution.
Example 1. Taxpayer B receives a $45,000 distribution from a section 403(b) plan on November 1, 2005. Taxpayer B is a qualified individual and treats the distribution as a Katrina distribution. Taxpayer B receives no other Katrina distribution from any eligible retirement plan in 2005. After receiving reimbursement from his or her insurance company for a casualty loss, Taxpayer B recontributes $45,000 to an IRA on March 31, 2006. Taxpayer B reports the recontribution on Form 8915 and files the 2005 tax return on April 10, 2006. For Taxpayer B, no portion of the Katrina distribution is includible as income for the 2005 tax year.
Example 2. The facts are the same as Example 1 of this section 4.D, except that Taxpayer B timely requests an extension of time to file the 2005 tax return and makes a recontribution on August 2, 2006, before he or she files the 2005 tax return. Taxpayer B files the 2005 tax return on August 10, 2006. As in Example 1, no portion of the Katrina distribution is includible in income for the 2005 year because Taxpayer B made the recontribution before the timely filing of the 2005 return.