From reading the actual messages, the "to prevent UI customization" in the HN headlines seems to be editorialization. They explain in the comments that it was to reduce bundle size and it produced a measurable improvement in load times.

> We are doing this to save bandwidth and startup time. Mangling allowed us reduce the size of our renderer JS bundles by ~13% (-1.5MB). This yields in ~5% faster code loading. Similar numbers apply to the main and extension host bundles.

These were private properties, not part of the exposed API. Plugins that depended on these were prone to breakage anyway, as is the case with using any private API.