Did anyone every had a use-case to allow third party developers hook into your own suitebundle/suiteapp? E.g. some process where a third party might want to inject code? if yes how did you solve that? (like in Wordpress they have the hooks API for exactly that use-case)

Probably a good use case for Custom Plug-ins https://docs.oracle.com/en/cloud/saas/netsuite/ns-online-help/chapter_3976781171.html

Hmm interesting. I'll check that out