* note the small 'p' used throughout here, since I'm referring to any smartphone running either Windows Phone 8.1 or Windows 10 Mobile.
Note that the device lists above are obviously not complete, they're just introducing the most popular devices in each 'family'/class. For the full list (w.r.t. Windows 10) see here.
Aside from the obligatory link to my Lumia 1020 proof piece about staying on 8.1, the interesting and most relevant box here by far is the green one in the middle, representing a fairly large slice of popular Windows Phones from a couple of years ago that many readers still own. And as per my recommendations earlier in the week, there are lots of reasons now, in May 2016, why it's worth putting up with a speed hit (of 'up to' 50%) in order to gain functionality and currency with Microsoft's Windows 10 services and ecosystem.
I state above that 'Updates will stop in summer 2016' because around that time 'Redstone' will become the 'production' build for all compatible phones and the official updates for this (builds 14nnnn etc.) will start being pushed out to general users. At which point the 'Fast' and 'Slow' Insider rings will move ahead to Redstone 2 (I'm guessing builds 15nnn) and the 'Release Preview' ring will become previews of updates to Redstone. Meaning that the 'Threshold' lifeline for older Lumias will have been severed forever. However, as i've said before, your 2-3 year old Lumia will still be on much more up to date code/apps than if you'd left it on Windows Phone 8.1, so at least you've eked out a bit more life. And, barring major vulnerabilities in Threshold being discovered , there's no reason why an Insider/Release Preview-updated Lumia 925 (say) shouldn't be very useable for another year or so, possibly more - it'll certainly be compatible with most of the new UWPs.
Hopefully the chart above is pretty clear and will help anyone who's still unsure about where their older Lumia fits into the grand scheme of things? Comments welcome, as always!
PS. Another FAQ might be "What's the future of All About Windows Phone?", of course. We're keeping the name and just de-capitalising the 'p' (where appropriate) and pluralising the last word (ditto). So "All About Windows phones" still works pretty well in terms of clarity, we think?