We added further support for bookable on the /biblio/{biblio_id}/items endpoint.. we should really replicate that on the /items endpoint including enhancing the support from just ?bookable= param to the q= param handling. I also think we should rename from bookable to effective_bookable because that's what the special handling actually uses now.
From bug 35906 comment 85 We should support the ?bookable filter on the plain /api/v1/items endpoint too. Also.. I'm tempted to rename it 'effective_bookable' to more clearly distinguish been effective bookable and localised item bookable fields. I'd love to see this also taken account of within q= as well as the local param option.. that could be a future follow-up though.
I like the idea to follow the pattern with effective_ here. Would it make sense to expose both, the item level information and the combined status from item type and item or is the latter enough really?