We do understand that this could create a potential incompatibility, that tools based on OA would not process BIBFRAME Annotations. That's a fair point. On the other hand, some of us think that this feature is important because of the potential simplicity it can provide, and if enough of us feel that way then maybe it is worthwhile to try to convince OA to allow this feature.
In terms of simplicity - I don't think any of this should be exposed to the content creators (i.e. cataloguers) or consumers - we have to have tools for metadata creation/display that are simple. So in terms of achieving simplicity in the data I believe it needs to be considered in terms of cost, rather than apparent simplicity. If tools for both creating, and consuming OA do not process bibframe annotations it means we have to build ourselves which is a cost to the community.
Regardless of compliance with OA I'd argue for consistency anyway - so I don't want to have to check each time I come to an annotation whether I'm dealing with a bodyliteral or a annotationbody - if I can always rely on one or the other it makes life a lot simpler.