I suppose they don't want to confuse statutory due date with the extended deadline (like the 2-month automatic extension expats are given for filing federal return).  When the final regulations are out, they may then formalize the extension procedure.  For now, anything that helps get people with offshore accounts/assets to comply at the individual level is good with the Treasury Department, especially since FATCA doesn't seem to be working out the way the government had envisioned.