possible ways I can think of

• deviate from mediawiki/wikibase codebase in form of a fork, which we will have to maintain
• create a mediawiki extension that hooks into mediawiki/wikibase to modify things (not sure if that is feasible)

In T314996#8145344, @Deniz_WMDE wrote:

possible ways I can think of

• deviate from mediawiki/wikibase codebase in form of a fork, which we will have to maintain

Seems feasible, another option could also be just another branch in the main Wikibase repository?

• create a mediawiki extension that hooks into mediawiki/wikibase to modify things (not sure if that is feasible)

This is similar to how some things (custom APIs) are already loaded in the wbstack/mediawiki repository.
As well as APIs, other hooks are used for the sidebar etc.

I believe there was also a desire to move this to its own extension.