You can absolutely add homeless Sims! I have some custom townies that I was hoping the game would use to run food stalls, etc. The way I set them up is:
1. Create the household in CAS.
2. Move them into an empty lot from managed worlds.
3. Immediately evict them from that lot.
You'll then have the option to create a new household to place on that empty lot, so you can repeat this for however many homeless Sims you want.
EA could also then add WAYS to help the homeless such as shelters, and city/town missions where both places could food, house, and clothes the homeless. PLUS DONATIONS!
This is a different use of "homeless" than we were using--we were using "homeless" as "not currently in world"--but these are great ideas! One thing you can do is build a shelter as another lot type (pool, library, restaurant, community lot if you have Eco Lifestyle) and then have your homeless rags-to-riches Sims sleep in those shelters. The library would probably be a great choice if you don't have Eco Lifestyle, as homeless people do sleep at the library and they could look for jobs on the computers and read books (maybe add some skill books, if the library doesn't have any?).
I know my friend slytherclaw72 has built a community lot with a shelter attached....
