I've made mention a couple of times that they should have scrapped this numbering scheme for something more sensible. For example:
First number(s): 7xx for low-end (such as the 520, 521, 620, and 625), 8xx for mid-range (such as 810, 820, 822), 9xx for high-end (such as 920, 925, 928, and the upcoming 929), 10xx for the high-end camera devices (1020), and 15xx for the super-sized devices (such as the 150; I'd say over 5 inches covers this)
Second number: Screen size could be used here, like 4 for the 3.8-4.9" devices, 5 for the 5.0-5.9" devices, then 6 for the 6.0"+ devices.
Third number: I would imagine this would be a little messy internationally, but my initial thought is to go with carrier variant here. They sort-of did already with the 92x devices, with the 920 for AT&, 925 for T-Mobile (until it reached AT&T), and the 928 for Verizon.
The only real problem (beyond the international use of the third digit) I could think of would apply to the tablet(s), since they've decided to give them the Lumia brand name as well. The upcoming one is the 2520, but my suggested scheme would make it something like the 2510x (25 for the tablet, 10 for the 10.6" screen, and x for the carrier). If they made all of the tablets carry one universal antenna (meaning cover all bands for all carriers), they could go 2510, I guess. They could also just use 1 for the 10" screen (since screens won't actually exist in the 1" realm), then go 251x, with the x again a carrier digit.
I don't know. Regardless, I like the idea of this 929. I'm not really thinking a 1520 would work for me, despite my reasonably-sized hands. My 920 fits perfectly in the side pocket of my jeans, while a 1520 would stick out of the top by maybe 1-2 inches. Even reaching the top-left with my right thumb's a bit of a stretch on my 920, but I think a 5-inch device would still be doable for me, especially if the cut down just a tick on the top and bottom bezels.