Here's the new, AppRaisin-derived data:
Here's the source page, in case you want to view the other slides, based on in-app ad display.
Now look at the devices mentioned - 9 of the top 10 used by 'enthusiasts' (think really active users of the ecosystem) are fully compatible with Windows 10 Mobile and all the latest UWP goodness. In fact, a proportion of the 19.6% 'other' devices are also compatible. At worst case (ignoring the 1520 and ignoring 'other'), we still have 75% of active devices in this 'view' either running Windows 10 Mobile or presumably about to upgrade when the user gets round to it. (They've had three months since Microsoft started telling people that the upgrade was ready.)
Maybe I'm making too much of this - but I wanted to put a market in the sand that takes the opposite stance to most other reporting web sites!
AdDuplex is right to point out, in its other slides, that there are huge numbers of users of low end and older Windows Phone 8.1 devices - tens of millions at least. probably in the hands of teenagers and the extremely undemanding. But these have very little influence on the ongoing Windows 'mobile' story* and neither should they. In my opinion.
* For the most part, they're using three to four year old phones and won't ever be able to upgrade to Windows 10 Mobile.