One product I think could have had success in the late 70s and 80s was using 8 bit micros as a pre-processor for COBOL. You could type and verify the syntax using a micro before you would submit the code to the mainframe.
A lot of data entry jobs in the early 80's was done on 8-bit computers that wrote the data to 8" floppies that were then read by the mainframe. Some other setups had tape output. I interned at a company that did input to tape, which fed an IBM 4341.
Most 8-bit micros had very poor data interchange capabilities, though. That was one thing the IBM PC and 'clone' ecosystem got right. Still, you could use a minicomputer for the job. Minis were often used for similar tasks.
