You'll see a very large backlash from the commuters, and it may have a very nasty side-effect for the airlines.
Most contracts have a "minimum day off" stipulation. If a commuting day would now count towards duty time, it's not a day off. Remember, Duty or "on call" is not rest - Whitlow interpretation. Therefore, a day off is ONLY one on which you did not fly OR commute, if commuting is now counted as duty.
So what happens to the guy who holds a 14 day off line, 16 days on, 4 4-day trips, uncommutable on BOTH sides for this rule? He just got chopped to 6 days off. Oh,,, wait,,, contract says 12 calendar days off minimum for lineholders.
2 choices: build all trips commutable, or remove me from one of my 4-days and pay protect me to bring me back up to 12 days off minimum. HUGE increase in staffing levels required.
Remember what I said in a thread a few months ago... EVERY SINGLE TIME you change a reg, there's fallout about 3 or 4 levels deep that NO ONE thought of when creating/modifying the reg.