Those who have successfully updated their Lumia 950 and 950 XL devices to 10586.29 won't be affected by Microsoft's move.
I've asked Microsoft officials if they have an estimate as to when they may republish the 10586.29 build. No word back so far.
Windows 10 Mobile 10586.29 was the first cumulative update to the Windows 10 Mobile build that Microsoft delivered on its first Windows 10 handsets. Microsoft made 10586.29 generally available a couple of days after Windows Insiders got the build for testing.
Update (December 16): A Microsoft spokesperson emailed me last night to let me know 10586.29 is back and available for download. The official statement:
"After momentarily pausing the Windows 10 Mobile update due to an issue with the update server that impacted the installation of the update on a limited number of phones, we have addressed the issue and will begin rolling out the 10586.29 update again."