Without purchasing new processors, Intel Software Defined Silicon will allow for activating additional hardware capabilities if purchasing a license/upgrade. The exact details don't appear to be public yet for what "upgrades" they will offer, but Intel is currently preparing the Linux kernel driver support.
Initially this Software Defined Silicon support appears to be focused on Xeon processors as opposed to license/upgrade features for Intel Core desktop/mobile processors. Yes, a decade ago Intel tried a similar approach in the consumer space with the Intel Upgrade Service that was short-lived and never saw Linux support.
The Intel Software Defined Silicon (SDSi) driver is for supporting the "post-manufacturing mechanism for activating additional silicon features."
The SDSi kernel driver exposes a per-socket interface so their user-space application can provision an authentication key certificate that is written to internal NVRAM, provision their "capability activation payload", and reading of the SDSi state certificate that shows the CPU configuration state for a given processor.
This Software Defined Silicon driver is just about the authentication and dealing with the SDSi handling but doesn't expose what Intel may pursue in regards to license/paid upgrade features moving forward. There is the patch for this kernel driver currently undergoing review. Additionally is this GitHub repository now public that just outlines the operating system interface for SDSi. Intel currently doesn't have an open-source user-space client or we'll see if that ends up being a proprietary software package if it will allow built-in purchasing support, etc.