WasmEdge is really cool -- I'm super impressed with the work they are doing and hope to eventually provide an alternative runtime backend to Extism using WasmEdge (maybe they'd like to help!)

To answer your questions: 1. Extism provides a specific set of host provided APIs, and currently we don't have support for user-supplied host functions beyond the ones we make available. This will change though, and we're looking for feedback. We held off because there wasn't a clear way to make it easy across ALL the languages we support.

2. Complex types are definitely supported, you need to encode the data into raw bytes and can use whichever format you want (only limited by which formats are available in host & plug-in languages..)

Eventually we will move towards the Component Model which will make the complex types story much simpler.