This doesn't require physical DRAM access, it's all software.
With ring-0 access, this lets you poke "even things walled off and invisible to ring-0 or the CPU itself" including things that the security processor tries hard to wall off.
Which arguably is a good thing. As a owner of the system I really should have complete control over it. But currently there is software I have no control over running at even higher privilege levels.
The only modern silicon that gives me full control over what code is running is some (or most?) microcontrollers.
And this isn't just a question of FOSS principle. Especially SMM is problematic by unpredictably taking CPU cycles away from your workload. This can mess up hard realtime workloads, such as found in CNC controllers. If you are running something like LinuxCNC this something you need to measure to figure out if a given computer is suitable for that job.
Whilst I like getting more control of my hardware, I really prefer if I can contain arbitrary software - sandbox it and compartmentalise it. If arbitrary processes can own your whole system, is anyone truly an owner?
You probably misunderstood the technical writeup (if you read it). This is modifying MMIO registers of the DRAM controllers. Normal user space (ring 3) doesn't have access to that. Nor does a VM guest. This needs host kernel level access to begin with. And that is the layer that should be in complete control of the system. There shouldn't be a hidden OS underneath that I can't replace.
So you might like Qubes OS, which isolates all apps into hardware-assisted VMs. You will still have all the access from the AdminVM, but arbitrary processes won't.
Pragmatically, we all want the MMU to work and for pointers to address the correct logical address. No one is keeping anything valuable from you by preventing this. It's not like a DRM scheme.
As I understand it, this can be used to access secrets of various secure enclaves on affected systems (potentially TPM in firmware, SGX, ARM Trustzone etc, depending on what the platform in question has). In which case it absolutely is used for DRM on some devices.
And as I pointed out in the comment you are responding to, there are plenty of other reasons to want complete control of my computers. Härd realtime behaviour is especially important to me, as is the principle of FOSS.
With ring-0 access, this lets you poke "even things walled off and invisible to ring-0 or the CPU itself" including things that the security processor tries hard to wall off.