I am playing in franchise and have about 8? Enclosures now, doing semi custom barriers using the null barriers more often than not, the main issues I get is guests being able to peer through solid rock to glance at cheetahs in a spot where it makes no sense because of some tiny crack or something you can only see from a specific angle #triggered.
I find one of the best ways to get around the basic enclosure gates is to just make a building or some form to overhang/hide it, alternatively you could branch it out and add a keeper hut inside to make it easier for your workers also, either way my zoo is not having performance issues having soo many custom pieces in it yet, My dingo habitat is entirely custom walls from the Australia pack, I using some of the new wooden wall parts and it goes all the way around into some rock walls that are also custom, in my Jaguar and Siberian tiger enclosure all their walls are just stone wall pieces and it works nicely for custom barriers also, I imagine you could make some wooden fences to keep larger more docile animals inside, like elephants or zebra, there are a lot of wooden parts in the game one could use to make fences, then u just save it as a piece and you could use it in some places, the custom barriers don't have to go all the way around an enclosure, just at like key viewing points potentially.
Either way I guess I can see why some people might want the wall tool since i guess in some cases it is a little easier to use, in my opinion however it is kind of annoying to use, I am very thankful for null barriers, I dislike how the barriers created using the tool tend to decay so quickly? They get very expensive in franchise mode also if you have a lot of enclosures to repair constantly, you need way too many staff to repair those walls all the time. Also another reason why custom barriers are superior they don't have upkeep.
I would not be opposed to new barriers added just feel like with null barriers its kinda easy to just make your own, doesnt have to be 1000 pieces, maybe just 4 or 5, good ones and you got yourself a barrier idk. Doors on the other hand, I can agree, we could use more, only having 2 is kinda weird,having a glass one would be weird but cool.