Sanders will not appeal to the middle class or better soccer moms who are trending liberal and have helped to flip suburban counties toward the Democrats. However, he would have more appeal to blue collar voters, as he isn't an obnoxious billionaire who despises workers and farmers, an over the hill swamp critter, an inexperienced small city mayor, or the Massachusetts answer to Hillary. Sanders comes from a humble background and, like him or not, he is the best orator of the lot. He has passion almost at a Trump level.
Sanders could flip MI, PA, and WI back to the Democrats, especially with a black VP choice. However, he won't play well in places like VA, CO, NC, and NV, where moderates play a big role.
I suspect the DNC will make the choice when no one has a majority of delegates. Those running about the country have only one shot, the first ballot. If one does not secure a majority then the Party will make the choice.