The downside is don't be shocked if the extra inch of legroom in Rows 10-23D/E (which have about 33" pitch) goes down a bit, so that rows line up. Likely it will be an extra 6 seats where the Y galley is now, with another 2 seats coming from the realignment of the D/E seats. That would net 8 seats and allow for 150 passengers, which is as high as Delta would want to go (without adding another F/A).