Form 4868 requires you to (on line 4) give an estimate of the taxes you will owe. The form's instructions say, "Make your estimate as accurate as you can with the information you have. If we later find that the estimate wasn’t reasonable, the extension will be null and void."
Because of the difficult situations many people face right now, it's helpful to have one less thing to worry about. Some people are sick, unemployed/furloughed, trying to save their business, healthcare workers working 80 hour weeks, away from home and unable to travel back, unable to meet with accountant, etc.
The threshold for finding of “unreasonable” is surprisingly lax in normal times. It’s no doubt going to be more lax now, especially if the discrepancy was remotely plausibly COVID-19 impacted (inability to use your normal preparer, access your mail, whatever).
I file the 4868 literally every year; I’ve never had any estimate even questioned, let alone overturned, despite sometimes being off by mid-high 5 figures (usually over, sometimes under).
The IRS seems content as long as you’re showing any reasonable intention to comply with your obligations. Everyone is afraid of them because of their power. That’s sensible. My experience (including two audits, one a TCMP audit) is that, while they move at government speed, they are quite reasonable and even helpful to deal with.
The reason for the reasonableness requirement is that in a normal year, you are required to pay that estimate on Apr 15 when you file the extension. If the estimate was too low, the IRS wants their pound of flesh.
In a year where no one has to pay until Jul 15, there is no point in enforcing that clause.
There is benefit to people in pushing the filing deadline even after the payment deadline has been changed as it does reduce the paperwork burden, especially for those who rely on paid preparers.
Form 4868.