I think it's possible, but I think you should add things like avocados, nuts, seeds, nut/seed butters, different oils like flaxseed, spirulina, cholorella, and other herbs to them.
Some veggies, like spinach, kale, and frozen broccoli are okay in smoothies, but a lot aren't. I think if you want to live off of smoothies, you should look into a raw food diet. Many raw foodists eat green smoothies for breakfast, and then meals based around raw produce! You'd be amazed at how tasty this can be!
Many people DO live off of juice, but I've never heard of any living off of smoothies. I'm sure it's possible, but I just don't think it's preferable....I like crunchy things :3