>> `hi-lock-interactive-patterns' as `permanent-local'.
>
> Agreed.  Even more so for hi-lock-file-patterns.

>> With `global-hi-lock-mode' ON, you will notice that highlighting will
>> be retained across reverts.
>
> Not any more after my patch.

Whether this change in behaviour counts as a regression, I am not sure.


>> 2. I think `font-lock-fontify-buffer' should be added to
>>    `hi-lock-font-lock-hook'.
>
> Why?

`hi-lock-font-lock-hook' adds the font lock keywords.
`font-lock-fontify-buffer' activates the keywords. 

>>    For some reason, `hi-lock-font-lock-hook' doesn't get called at all
>>    (even though it is added to the `font-lock-mode-hook'.)
>
> What was your test case?

For the sake of discussion, I undid your patch.  

Apply this patch and re-load hi-lock.el.