There is no plan to create a npm package similar to mediawiki_selenium. That said, instead of such package, all shared code now lives in mediawiki/core. That is a deliberate architectural decision. As far as I know that pattern is already used in PHP and JavaScript unit tests. @Hashar could correct me if I am wrong.
Discovery team has found another API package instead of nodemw. mwbot that has some features they need. You can follow T181284 for more information.
If nodemw/mwbot does not have features we need, we can always contribute upstream. If upstream proves to be unresponsive, we can always fork.