I wouldn't say there is a canonical baseline model but your example would be a reasonable place to start. Weighted average by sample size is a straightforward m

I wouldn't say there is a canonical baseline model but your example would be a reasonable place to start. Weighted average by sample size is a straightforward modification. Just using the most recent reliable poll would also be interesting. I think most of the extra value you could add would be from analyzing the poll data to get a sense of which polls were unreliable.