There was a version of VI eventually called levee that was written by students @ UW Madison in the early '80s that went with their unix command interpreter running under UCSD I.5 running on the 8510a Teraks in the computer lab. These 5 or 6 computers were used by the beginning Pascal programming course between 1982 -- 1985.. The system was called OSY, and I found it quite remarkable that they were able to simulate a unix like experience on the machines. Needless to say, levee was written in Pascal, but was later converted to C and ported to Windows and Linux. Very small footprint.
Now, if I could only read all my 8" floppies, and if they are still good...
I also at one point had the source to the older unix vi, but from what I recall, it required some system calls that were not available on Venix/11 which I was running on the Terak 11/23 system I had at the time.