Directly answering the question your stakeholders will think but not ask
Another fun read! Reminds me of all the conversations over the years I've had with management and product about the "ROI" of investing in a design system.
One thing I'd add to your "Why engineering should care" section is that a design system should really be considered a part of a company's "UI platform". Engineering leadership often has more backend experience than frontend, so they will be very comfortable with investing in backend platforms, yet unsure of what equivalent investments look like on the frontend. They may even have had negative past experiences with past frontend investments, such as migrating between libraries, that make them inherently skeptical of other supposed investments like design systems. Tailoring one's description of a design system's benefits to the background of engineering leadership can help get their buy in.