thanks for sharing!
I don’t agree here.
According to my experience (corporate intranet, e-commerce and fintech) I was involved in projects where the UX was measurable.
Defining UX KPIs is a good starting point IMO and you have also data to lean on for measuring the UX strategy performance.
We measure UX KPIs such conversion rates, time to accomplish the task, the user requests such the password recovery, user issues addressed to the customer care (call-centre, emails, twitter etc). Those figures provide a clear overview of what are the UX strategy performance.
Of course, you have also other KPIs to add such the environmental ones (eg if the product is shipped in different countries), technical ones (eg if the product is designed for cross-device targets), but this, according to my experience, is not a blocker to measure the UX.
Superstar designers like Luke Wroblewski are pushing a lot this topic (https://www.youtube.com/watch?v=xiyOTcVHqHw)