This update that is "held up by carriers" so to speak, is firmware, as admitted by Adam Frix.
"The new firmware, version 01078.00027.15506.020xx, features several improvements to the phone’s stability, performance, SD card support, automatic display brightness, camera issues and a fix for a 4K video problem that was causing stripes to appear while playing a video."
Perhaps we need to understand what firmware is, since this is a firmware update.
Firmware is the low level code that tells the Operating System HOW to talk to the actual hardware devices, like the camera, the GPU, CPU, Display, and it also includes Bluetooth, FM Radio, LTE, GSM, CDMA and other radio bands as supported by the hardware specific to a particular device. The 4K video problem was an issue with an error with the Windows 10 Mobile OS unable to properly communicate with the GPU, because of an error in the Firmware. Same with automatic brightness, SD card (hardware that needs firmware to communicate with it), etc.
Firmware in a phone is like the BIOS in a Laptop or Desktop PC. The BIOS (Basic Input/Output System) contains the low level code that lets an Operating System talk to the actual hardware of the device. Without it, the OS cannot talk to the CPU, GPU, Storage, RAM, Cameras, or anything else that is hardware built into the system board. External devices that you plug in are different, and just require OS drivers. Anything built into the SOC and original hardware will require this low level code.
So at absolute BEST, MS is guilty of wrapping up non-radio base functionality fixes--SD card, display, video playback bugs--with radio fixes that require carrier approval, causing the VERY delays that MS promised would not plague Windows 10 Mobile and later devices.
You can't separate radios, SD card, display, GPU, etc. out of the firmware. Those things can't be handled by the OS, because the OS needs firmware to know how to communicate with those devices.
But no matter what, this directly contradicts Microsoft's story of not too long ago:
Microsoft will bypass carriers, push Windows 10 updates directly to phones | PCWorld
yes, if MS says that "well, we have this update, and it includes non-radio functionality fixes, but we don't know when you'll get it, that's up to the carriers," then MS has some 'splaining to do with respect to their original story. The world is not just about security patches, especially not on a new phone like this.
I notice the article is how Microsoft will push Windows 10 updates directly to phones without carrier intervention. That has not changed. All Windows 10 updates still go through without carrier intervention.
However, Firmware, as explained above, is not part of the Windows 10 OS. Just like the BIOS is not part of the OS of a PC. You can use the same firmware on a phone, and boot either Android or Windows Mobile without changing the firmware. The firmware just helps one of those OSes talk to the hardware. It's like we saw HTC put out a Windows AND and Android version of a phone recently. If HTC needed to do a firmware update, it wouldn't go through the OS to do it.
My laptop was not compatible with Windows 10 until I upgraded the BIOS from the Manufacturer. Even with Windows 8.1, I was getting the dreaded Blue Screen of Death rather frequently. I decided to test Ubuntu on it, and, guess what? It locked up and froze up frequently when doing the same types of tasks. Turns out, it needed the BIOS updated to fix the issue, and it wasn't Windows 10's or 8.1's fault at all. The BIOS was causing problems with how an OS, any OS, communicated with the hardware.
People get confused with Microsoft updating firmware and/or OSes on Lumia phones. They don't get confused when getting an OS update or BIOS update on their computer. Why is that? Because the BIOS/firmware comes from the manufacturer, and the OS comes from Microsoft (if it is Windows). In this case, Microsoft is the manufacturer to update the firmware, and the OS provider to update the OS, but that doesn't make the two the same thing at all. Just because the pet store sells both Dogs and Parakeets does not mean the dog will be able to fly.
Microsoft never made the promise to provide firmware updates without carrier obstruction. However, they did make sure that they were only working with carriers that promised to help and not hinder, which means I don't expect any of the 950s to get left out.
Why aren't all the phones getting updated already? Microsoft rolls out firmware in waves, starting with a region at a time, slowly. This is so that if there are any further problems discovered in the firmware, it will affect a smaller number of people, and it can be corrected before continuing the roll-out.
I hope that clears up some of the confusion.