I think 5.5" is the current sweet spot for smartphones, but I don't think it will happen with the Lumia line. Unlikely they will squeeze in a third size between 5" and 6" and I don't see the 5" phones getting jettisoned or the 1520 successor getting smaller. Maybe another OEM might go that route but I wouldn't hold my breath at this point. Even if Samsung were to bring a phablet to the party, the Note 4 is 5.7" which may be about as close as any large manufacturer would get to that size.