How many phones do you folks think will be in Microsoft's Lumia line per cycle?

So we've all seen Nokia's strategy with the Lumia line; lots of phones, lots of form factors. Do you guys think Microsoft will keep this up, or will they take more of a Surface-type strategy with just two, or maybe three models? Or heck, since there's only one SoC platform per cycle, just one? I'm not entirely sure we need a 520, 620, 720, 820, 920, 1020 and 1520 lineup, but I think it would be a shame to waste the opportunity created by the incredible potential shown by the low-end Lumias. If Windows Phone has a definitive, obvious strength against Android, it's got to be the degree to which the Lumia 520 just shames low-end Android devices when it comes to UI smoothness and performance.

Personally, I'm thinking maybe the sweet spot is a 520 successor, a 720 successor, and a 1020 successor per year is the right call going forward. With a possible option for continuing the 1520 line. What think, Tribe?