It would be an excellent experience if I could invite my friends to my shelter.
When we do matchmaking we can appreciate each other's outfits which may potentially increase the value of the outfits and make the outfits more attractive to buy. : )
We can buy some custom decorations located in the shelter. Like flags designed by players hanging on the flagstaff. The decorations might have some benefits if friends come and interact with them (with cold down time) or just be there for nice looking. there can also be some interactive furniture set for two players like a chess game or card game besides Rubik's Cube.
We can visit offline friends' shelters to help them collect some food & materials and gain some rewards like getting 10 percent of materials from friends. Knowing Farmville is a social network game that makes many interact with friends this function will increase the player engagement rate. People will be more willing to run the game daily.
All of this is just a suggestion. The specific details need to be modified and designed by devs. But I'd like to hear other players' voices. : )