While I use vi all the time I don't think I'd want it as a text editor on a C128. Given the fact that vi and its ancestors was written for use with systems of limited text presentation capability, it seems like a step backwards (several, actually). In particular, the need to constantly jump between command mode and text edit mode using character keys was due to limited terminal capabilities. Why hamstring oneself in that fashion on a system that natively supports a wide variety of control keys (e.g., F1, ESC, etc.)?
