Intel researchers discovered that Intel graphics processors allowed userspace to modify page table entries via writes to MMIO from the Blitter Command Streamer and exposed kernel memory information, resulting in possible privilege escalation and information disclosure vulnerabilities. A local user could use this issue to escalate their privileges on the local machine.
It's i915.mitigations
If my interpretation is correct, that means as long as you're using an up-to-date, patched kernel with standard mitigations enabled, the extra security layer Intel added is no longer necessary. It could expose another bug not yet covered by patches, though, as the heavy-handed patch probably also prevented more security issues.
So, they decided to remove this (IIUC third) level now.
Since you're doing the research, you tell us. Is NEO_DISABLE_MITIGATIONS (the flag mentioned in TFA) related to i915.mitigations, and if so, how?
TFA mentions that Intel ships prebuilt driver packages with this NEO_... flag set, and that Canonical and Intel programmers talked at some length about the flag.