What a saga. Took me 4 days to convince Gutenberg I am not a direct threat to the literate world so I could view the page. That produced interesting results, confirmed by my own local tests.
Webkit has a bug report about this, Gecko has supported since 1.9, and ie has no support, so all explained, but Opera doesn't reconcile: I read your post as saying it is applied (on a Mac) but it isn't here on a PC. On checking Presto 2.9 is not supposed to support adjust, although other parts of the css3 Fonts module have been implemented for some time. Meanwhile, Dragonfly couldn't decide whether to report the explicitly set value, or just "none", and I couldn't find anything to indicate it would/should be different on a Mac. Quite a mystery!
But the limited implementation is such a shame - like you I think this is such a useful property - and from a design perspective as well as accessibility/usability. And your link to more complex text scenario just emphasises how really useful it could be.