[trynewideas]

Reintegrating the parser into Mediawiki's PHP core goes beyond performance. Many prominent MW features -- particularly the visual editor, translation functions, and mobile endpoints -- depend heavily on Parsoid/JS, which required running it as a Node.js microservice, something not all smaller (or especially shared-hosting wikis) could manage for quite some time.

Bringing Parsoid closer to core makes it easier for non-Wikimedia admins to use more of MW's modern core features. The performance gains are a nice bonus, and I suspect are related to the general improvements into PHP 7.2.

[dingdingdang]

Performance gains of "Parsoid/PHP ... roughly twice as fast on most requests as the original version" are bit more than a casual bonus and into territory of pretty dang awesome in my book.

[trynewideas]

I totally agree, but on wikis of a smaller scale it's not a difference of performance, it's potentially being able to use some of these MW components for the first time. It could be 10x faster than Parsoid/JS and that's irrelevant compared to being _possible_ on a service that won't let you run Parsoid/JS.