I hate the idea of a veto for anything except the top 1-2 brackets. For lower-rated and middle-rated players, part of the point of ladder is to push your comfort zone so you can learn about different kinds of maps.
For higher-rated players, if they prefer to have a veto, we should respect that. If adding a veto means there will be more high-rated ladder matches, then it's probably a good thing.
Also, or in the alternative, I think it would make sense to give 1300+ players the ability to "opt-in" to the 1800+ pool. It would be bad if we threw them all in to the 1800+ pool because not everyone wants to learn build orders for 6 new maps every time the ladder pool changes, and we don't want to chase away 1500s. Some people only want to play 5-10 matches per month. But if some of them are especially active and would prefer the larger pool, allowing them to opt-in would be good.
Another way to do it: get rid of the 1300+ pool, those players would all be forced to use the 1800+ pool. BUT they get at least 5 vetoes. By default, 5 of the vetoes are applied to the 5 "1800-only" maps. The 1300s could go into the veto menu and change it up. So if they never bother to meddle with the veto menu, they get the vanilla 1300+ pool because of vetoes. BUT they can easily move the vetoes around (or just veto nothing at all) if they take the time to open the menu.