We did main dining on the last TA. It did not work out great for us.
The time changes made it feel like the days were just too short.
Also, DD's LOVE the shows. The were falling asleep at the shows. To be honest they don't care about the food. They like the dining rooms for the fun but they order the same things every night anyway.
The Dine and Play program has made late dining great! About 45 mins into dinner CM's from the kids clubs come to the dining room and pick up the kids. It is great for us. DD's are wide awake for the shows, they come to dinner for a little bit and then head to the clubs for either fun or down time. After dinner we pick them up based on what activites are going on. DD 8 tends to close down the clubs every night where as DD 4 likes to comes back to the room earlier.
There are not that many port days but main dining (again, esp with the time changes) makes you have to be heading back to port sooner. Take pirate night for example....you have to be back on the ship and ready for dinner but since there is no show that night (not till deck party at 10:30) then you can head back to the ship closer to 7 vs 5 for dinner.
Our tablemates last time were late to the main dining. They were on a
DCL excursion and there were people who were late getting back to the bus. They waited for the people which caused everyone to be late getting back to the ship. The one guy with us was VERY unhappy. It was not a show night so they would have been better off not having main dining and not stressing themselves out.
I know other people love main seating but for our family it worked out better now that we do late dining.