Steve sold his store (and the name) to a group of investors in the mid 1980s who wanted to franchise it. According to Google, there is a Steve's Ice Cream in Faneuil Hall,; I don't know if there is a connection with the original. Steve's Somerville (MA) location was a mecca (I think that I wrote about it when we were discussing what you would stand on line for). With the sale, I believe that he couldn't open a store using the name Steve, so in a few years opened Harrell's near Harvard Square. Steve not only "created" mix-ins, but had high quality ice cream - super-premium. Cold Stone and Marble Slab are pale imitations, psuedo-high end, aimed for shopping centers.
I think that Toscanini's in the best in Boston now, but Christina does (deservedly) have its fans. In San Francisco, there is (or was, haven't been for awhile, Double Rainbow).
The question is why is Chi-town, such an ice cream shy town. Evanston or Hyde Park would be great markets for a high-end home-made parlour.