Having the vet career would be so interesting! And the animal shelter as a lot option would be wonderful. That was something that I felt was missing in The Sims 3 Pets EP. I didn't like that you only had the option to adopt an animal from a neighbor or adopt off of the computer. I know that these options are realistic, but I feel like a lot of people who rescue go to an animal shelter. I don't know how a volunteer option would work, but they could make it a very low paying teen job. Fostering would be a great idea, but I don't know if they would put that in there. And a sick option to go with the pets and vet career? Yes!
As someone who owns a pet, all of these options would make the gameplay so realistic for me and I would absolutely love it if at least some made an appearance in an EP.