Yes, the proxy approach would impose some requirements towards validated beans, e.g. having a default constructor, being non-final and such. It could be made pluggable, though, allowing to provide custom strategies specific to your bean types.

That being said I'm more leaning towards a de-typed approach (a bit like 2). But this will need more exploration and I don't think we can do it in the time remaining for 2.0. We can explore it in the reference implementation, though, so it can be added in a future revision. If you feel adventurous, you may give it a try and create a PoC within Hibernate Validator?