They’re stuck working with the FEC due to the complaint alleging that their spam rules are illegal de facto donations. At this point, they’d want to make sure any major changes to political email filtering are acceptable to the regulator.
Also by asking the FEC to weigh in and approve this before moving forward, google is in a much stronger position: if they’re not approved to move forward, the FEC can now be the bad guy; if they do approve to move forward, then they don’t get hit later because the FEC gave the stamp of approval.