Per today's discussion, we will be doing the HTML retrieval endpoints based on Parsoid output, not the PHP parser. This raises the question how the equivalent of ParserCache will work for that. For Parsoid/JS, we are using Cassandra via RESTbase for caching. For Parsoid/PHP, we currently have no ParserCache-equivalent.
We could think about doing this without internal caching, solely relying on the web cache. But this raises the question of purging. MediaWiki uses active purging for cached URLs. For this, MediaWiki needs to enumerate the URLs to purge, which is currently hardcoded in Title::getCdnUrls. Bucketing would probably make this a lot saner. We need a plan...