That won't solve the problem of table turnover. People don't eat salads at the end of the meal,they eat them before the meal. You get a party of two, one substitutes the salad before the entree, the other gets the dessert after the entree, and they share. Then they spend longer at the table without shelling out any extra cash.
There is speculation of that being the reason appetizers were removed. I don't know if that's why or not --- Personally, I think it was just a matter of cost savings for Disney. Just like they eliminated the tips being included, which clearly has no impact on table turnover.
But I disagree that allowing a salad hurts table turnover. Dessert is not even ordered until after the main meal is finished. And people will "linger" over a dessert much longer than they will a salad. And finally, a salad can basically be served simultaneously with the entree.
Overall -- considering the families/couples that will skip the dessert and just get salads instead, those people will turnover faster than dessert tables. So while some families turn over slower, other families would turn over faster.
But fine -- Then how about allowing a side-dish to be substituted for dessert? Side dishes cost the same amount as desserts. And side dishes do not hurt table turnover.
For example, at Les Cellier, the $4.99 wild mushroom risotto instead of the $6.99 cheesecake.