Flexowriter was VERY before my time. State-of-the-art circa 1980 was the DEC LA120 (DECWriter III), a dot-matrix printing terminal with a logic-seeking printhead that absolutely smoked the neighboring LA36.
There were Selectrics set up as terminals, though, as the mechanism was well-suited for it. I think IBM called it a 2741. I never saw such a beast, though.
All that was needed to make a Selectric into a terminal was essentially a box to take the electrical signals of hitting the keys (that triggered the correct letter on the ball to strike the ribbon) and amplify/send them to an interface into a device that could take TTY. Early word-processors and cold-type machines used this since those Selectrics were ubiquitous and dang durable.
There were Selectrics set up as terminals, though, as the mechanism was well-suited for it. I think IBM called it a 2741. I never saw such a beast, though.