So what would you expect to see when there is an update? Flashing lights, the newest lines in red, or what? I'm not trying to be facetious -- OK, maybe a little -- but from a user's standpoint, what's the difference between having the same lines redisplayed every n seconds until the file is appended, at which time the oldest line will be removed, everything else will move up, and the latest line will appear at the bottom of the list?
If you need a clearer indication that things have changed, then you could use [man]filemtime/man to record the last modification time of the log file (in a DB or something?), and each time the script is called check to see if it has changed. If so, tail it and output the result, or whatever you want to do to draw attention to the fact that it has changed.