Thanks for your comments!

>
> Also, the direction only changes at BOB and EOB, right?  IOW, C-v and 
> M-v don't change the direction, right?  If so, the text leaves that 
> unsaid.
>

No, with isearch-motion-changes-direction non-nil, M-< and C-v change the 
direction to forward, M-> and M-v to backward.  IOW, C-v is a faster 
repeated C-s, M-v is a faster repeated C-r, M-< is a faster RET M-< C-s 
C-s, and M-> is a faster RET M-> C-r C-r.  This is, I think, what a user 
would naturally expect, but I guess your preference is to leave the 
default of isearch-motion-changes-direction to nil (I would prefer to set 
it to t).

I attach the updated patch, in which I included your other suggestions.