The pace of Japanese publication is crazy - an average of three novels a year (sometimes four). Manga distributors in the west try and keep a similar release time-frame to Japan, so I wonder if they will with light novels or not?
Personally if I was Yen Press, I would try and see if the publication could be sped up a bit by releasing the novels in omnibus editions (with one English paperback containing two of the original novels). If a release pattern of 2/3 a year could still be upheld like that, then we could have the entire Index series (first 22 novels) by 2019 (if we assume that the first volume will be out before the end of this year - as Winter can mean early 2015). Then, publish SS as a single volume in 2020, before beginning New Testament.....dear Arceus, you're right. Even with that sped-up strategy, by the time we even get to begin New Testament, Japan could have as many as 26 novels (if it does go on for that long). Even if we do get the 3 novels a year, I'll be in my 30s by the time we finish the main series and knowing Japan's crazy light novel series lengths, 40s before we finish New Testament.