Parsoid has its own extension API - see https://www.mediawiki.org/wiki/Parsoid/Extension_API.
The PgaeImages extension needs an update to work directly with Parsoid so that we can switch Wikimedia wikis to use Parsoid instead of core parser in late 2021.
The Parsing Team will work with you as required.
Looking at the code, it appears that the Parsoid Extension API needs to provide a suitable entry point or equivalent hook for the hooks this extension currently uses. But, the actual parser API use is fairly minimal and should translate over fairly easily with some minor abstraction / twiddling of some method signatures.