From the Conversations piece:
Windows 10 Mobile is just the start of the journey, as with automatic updates you’ll always have the latest and most up-to-date version on your phone. The following Lumia 435, Lumia 535, Lumia 640, Lumia 640 XL, Lumia 735, Lumia 830, and Lumia 930 smartphones will receive a free upgrade when available
So, essentially, those smartphones released in 2015 or with guaranteed horsepower and on the Snapdragon x00 series of processors. The Lumia 1520 is again absent, and I can only think that it either didn't sell enough to be worth testing or is being given special treatment because of the screen size and the need for UI reworking (though it seems fine on the Insiders Preview). Or perhaps some kind of Continuum Lite is being tested for this? Here's hoping.
What of the rest of the Lumia line-up? Assuming that the OTA updates start rolling out for the phones above in November or December 2015, here's my best guess, with (mainly) all the Snapdragon S4-based devices (which will need a little more testing and optimisation), plus a few others:
- Lumia 920
- Lumia 925
- Lumia 820
- Lumia 720
- Lumia 620
- Lumia 630 and variants
- Lumia 625
- Lumia 520 and variants
- Lumia 1320
- (and yes, Lumia 1520)
What of the Lumia 1020 then? This is still a wild card, given the camera requirements, as I've investigated before, but Windows 10 Mobile Camera is getting there, so hopefully it can be batched in with the others above.
For anyone thinking I'm being too pessimstic in terms of time scales, remember that anyone who's keen enough can just jump on the Insiders Preview and jump all the queues. So, in that sense, Microsoft can take as much time as it needs to - unlike with previous OS updates, there's zero hurry here, at least in terms of pressure from enthusiasts!
There are some other oddities missing above, including the Verizon Icon, the resource-starved Lumia 530 and all the non-Lumia devices, so we'll have to see how that plays out. Despite renewed interest in Microsoft's longstanding UpdateAdvisor utility on the Internet today, some devices are just beyond upgrading, short of relaying their firmware from scratch via a PC.