AdDuplex released its latest report for October 2017 for Windows Devices. The AdDuplex interactive page shows a variety of OS information on different Windows Devices. Their report gives a clearer picture on the "results of the first week in Fall Creators Update lifecycle and take a final snapshot of the Windows ecosystem on phones as we know it."
Based on the AdDuplex Windows Phone October 2017 report, 73.8% of Windows Phone owners are still running Windows Phone 8.1, followed by Windows 10 Mobile at 20.9%, and Windows Phone 8.0 and Windows 7.x users in the bottom sharing single-digit usage percentages. AdDuplex did note an interesting tidbit about Windows Phone; that there hasn't been a significant drop in "overall OS version share." AdDuplex surmised that that might be because equal numbers of Windows Phone 8.1 and Windows 10 Mobile users are switching phone platforms.
With Windows Phone being discontinued by Microsoft, it appears that a lot of users are not in any particular rush to switch platforms right away. From a recent OnMSFT poll, a majority of respondents are still waiting for the bitter end of Windows Phone. Since the only Windows Phones that will be receiving the Windows 10 Fall Creators Update are not of the phones in the chart above, it's safe to say Windows Phone users will likely go to Android or iOS at a faster rate in the next few months.
Besides Windows Phone, the AdDuplex showed a sharp increase in installations of the Fall Creators Update on Windows 10 PCs and Surface devices. It is hard to say if the Fall Creators Update will continue the sharp rise that AdDuplex reports, since the Fall Creators Update was only officially released a week ago.