Ways to get tab-completion working in KSH, in vi mode. (NOTE: see here to find out what version you have)

AT&T ksh-88

First run set -o vi viraw.

AT&T ksh-93

First run set -o vi.

public domain ksh (pdksh)

First run set -o vi-tabcomplete. Or you can use set -o vi-esccomplete, and then you get: