"SER-P-i-m-p-ressionpossibilityrank" would also be fine. It won`t be the only factor, so I used "possibility". It triggers the badword filter by the way^^
I used "exposure" because it has been used in this thread before and to avoid a confusion with "pageimpressions".
I used "rank" to highlight the dynamic/liquid nature people already know from pagerank. Therefore I chose a similar name.