If you need some additional special-purpose features, my recommendation is to stick with Agenda and use hyperlinks for extra stuff. Full disclosure: I’m a cofounder of CogSci Apps Corp. which makes Hookmark. With Hookmark, you can bi-directionally link your Agenda notes to tasks in OmniFocus, Things or any other app that is link-friendly. Same goes for if you need to associate graphics — e.g., in Sketch , OmniGraffle. Even without Hookmark, you can include links in Agenda to the items out there; and many apps have linkback fields. E.g., OmniFocus tasks and projects have notes fields.
Agenda is a link-friendly app. The Agenda co-founders are signatories of the Manifesto for Ubiquitous Linking.
Compare: Using Hookmark to Integrate Agenda with Other Apps and Resources - Talk - Agenda Community.