Member Wikimedia\Parsoid\Config\DataAccess::doPst (PageConfig $pageConfig, string $wikitext): Parsoid should be able to do this itself.
Member Wikimedia\Parsoid\Config\DataAccess::fetchTemplateSource (PageConfig $pageConfig, LinkTarget $title): TemplateRequest also returns a bunch of other data, but seems to never use it except for TemplateRequest.setPageSrcInfo() which is replaced by PageConfig.
Member Wikimedia\Parsoid\Config\DataAccess::parseWikitext (PageConfig $pageConfig, ContentMetadataCollector $metadata, string $wikitext): Parsoid should be able to do this itself.
Member Wikimedia\Parsoid\Config\DataAccess::preprocessWikitext (PageConfig $pageConfig, ContentMetadataCollector $metadata, string $wikitext): Parsoid should be able to do this itself.
Member Wikimedia\Parsoid\Config\Env::getBehaviorSwitch (string $switch, $default=null): Does this belong here, or on some equivalent to MediaWiki's ParserOutput?
Member Wikimedia\Parsoid\Config\Env::getWrapSections (): Does this actually belong here? Should it be a behavior switch?
Member Wikimedia\Parsoid\Config\Env::setBehaviorSwitch (string $switch, $state): Does this belong here, or on some equivalent to MediaWiki's ParserOutput?
Member Wikimedia\Parsoid\Core\SectionMetadata::setExtensionData (string $key, $value): When more complex values than scalar values are supported, TOCData::__clone should be updated to take that into account.
Member Wikimedia\Parsoid\Core\TOCData::setExtensionData (string $key, $value): When values more complex than scalar values get supported, __clone needs to be updated accordingly.