Interesting idea. To some extent I often do fairly well at remembering who the OP is by their avatar. But I think what I usually feel is more important for me to remember is what the discussion of the topic is about. (I have been known to wander off topic at times 
)
In any case I think it would be possible to put together a few lines of JavaScript that gets an OP identifier (name?) and uses that as a CSS selector to apply style to the name / avatar where it appears in the topic.