The replies were mostly about Daniel's thoughts Andrew but I'll give my thoughts on a rating system now.
Firstly you are right that once a show is picked up it usually takes about six months to a year to get itself reading for airing. Most showrunners now like to have most episodes in hand and ready to go before even their first episode airs so that there won't be any delays in the airing schedule. There are still sometimes problems and delays but for the most part I think this system has worked well in helping keep the shows on MZPtv reliable.
I'm working on limited knowledge here so don't take what I say as gospel here Andrew but...
My knowledge of the poll system on the board is that it isn't intelligent enough to produce reliable results. Anyone can vote in a poll so what's to say that person will have read the episode. I'm not trying to call anyone idiots or say that this will happen but it is a risk. The other problem being that people may not base their rating on the episode but rather other factors that would be unfair to both the script writer and the showrunner.
Something that has been talked about in the past and that I agree with is that labelling a script with some arbitrary number doesn't give a true representation of the script. It was spoken about at length in one of the podcasts I participated in and there were some very good reasons brought up that explained why that was the case. For me it's much more helpful and interesting to hear from people about what they enjoyed and what they felt didn't work and why. Another point to think about Andrew, would be that if you were writing a script would you rather someone just gave you a mark of 4 for your first aired script or would you want to hear all about how your dialogue came across and how captivating your action was. The answer should be obvious and it's the same answer that any writer on here would give. An example being that people might mark it down for having a lot of SPAG, or maybe because the idea was flawed, or maybe because there was a major plot hole that wasn't dealt with. Without someone taking the time to explain their reasoning nobody is going to know why some nameless member scored a script the way they did.
While it might result in more people getting involved in some way, the reviewing numbers have been down across the board, I just don't see it being something that would benefit anyone.
So that when the writer looks back over their season they can see..."Oh, most people liked this one and that one"...
I just don't think those numbers would ever be reliable enough for this to actually be something worth looking at as a showrunner. Instead hearing people's thoughts would be much better for writers and showrunners.
There already exists polls for "Favourite Episodes" when people reach the end of a season so I think that covers giving a showrunner an idea about which scripts were most popular.