Kobo evidently are doing some analysis on completion rates, and published a report last year aimed at publishers using analysis based on similar metrics:

http://cafe.kobo.com/_ir/159/20149/Publishing%20in%20the%20E...

Further numbers into completion rates split by region and genre also from Kobo made their way into this nytimes article earlier in the year: http://www.nytimes.com/2015/02/05/arts/international/keeping...

I'd be interested in the raw data, particularly also from Amazon based on Kindle ebook read completion though I imagine that won't get shared.