With all the important holidays in the middle of April (Emancipation Day, Patriot Day, often Passover and Easter, my birthday, Kareem's birthday, my lifelong friend Tim's birthday, Jayne Mansfield's birthday, the Queen's birthday, etc.), they should make it simple by saying, "File your taxes on or before April 15 (regardless of when the important days are), or file for a filing extension." Done.
My friends who are tax preparers would love it. This year the weekend is perfectly positioned for their celebration of the end of tax season, but the stupid extension due to holidays wrecks that idea. The filings could have been done by April 14, but some of their clients are lazy and clueless.