Microsoft is determined to boost the adoption just-unveiled Windows 10 OS as much as possible. In addition to offering a free copy of Windows 10 for the first year of availability to anyone with a Windows 8.1, Windows 8 and Windows 7 license, the company is set to bring the OS to as many current mobile devices as possible.
In a blog post by Microsoft's own Chris Weber the low-end Lumia 435 is quoted specifically to receive the OS update. The article also confirms that the midrange Lumia 735 and the top-tier Lumia 930 will join the Lumia 1520, which we all witnessed at the press conference to be the pioneer Windows 10 smartphone.
The stated model numbers are more of a representation of Microsoft's plans for Windows 10 to span the majority of the lineup, rather than an exclusive list of devices that will get it. Meaning that your precious Lumia 830 is very likely to be on that list, for example. And also implicating that older phones may be left out.
The probable limiting factor may turn out to be the low amount of RAM on older smartphones. A multitude of older Windows Phone 8 and Windows Phone 8.1 devices came with only 512MB of system memory, which may have been sufficient for those OS releases, but it's unclear if it will handle the future...