Speaking of mode indication, nvi (vi found on FreeBSD) also has the option to show the current mode. It shows the mode both in insert & command mode; vim (6) explicitly indicates only the insert mode. Mode indication (in an editor) is a nice thing to have, though its lack does/would not bother me.

I have had not much experience w/ ksh88, but its vi mode seemed to be better than that of bash [23]; haven't used ksh93 much. Still, as you say, vi-mode inidication in a shell is much desired.