Microsoft has announced that all Windows 8 or 8.1 phones will be upgraded to Windows 10. However, this statement also comes with a twist which states that even if the phone is running on Windows 8 or 8.1, it may not be upgraded to Windows 10 if the hardware does not support it. The statement comes with a line "Today's Lumia phones", which could mean a lot of things. More of a possibility shows that the Lumia phones which are more than two year old, but running on Windows 8/8.1 may not end up getting Windows 10.
Most probable list can include Lumia 435, Lumia 735 and Lumia 930.
The update could be supported on the following devices -
1. Lumia 520
2. Lumia 630
3. Lumia 635
4. Lumia 530
5. Lumia 1020
6. Lumia 1520
7. Lumia 830
8. Lumia 930
9. Lumia 1320
10.Lumia 526
11. Lumia 620
12. Lumia 636
13. Lumia 638
14. Lumia 720
15. Lumia 730
16.Lumia 810
17.Lumia 820
18. Lumia 822
19. Lumia 435
20. Lumia 920
21. Lumia 925
22. Lumia 928
23. Lumia ICON
24. Lumia 430
Please note that this list is not supported by any confirmation from Microsoft. This is based on what Microsoft has stated about the update process. Some of the devices in this list may get omitted or some newer ones may be added.
Incidentally, Microsoft has also come on record that all Windows 8/8.1 devices with at least 512MB RAM are proposed to be upgraded, but with varied functionality.
Live....and Let Live!