Once this is working, I believe it will be possible to reimplement the driver side using only the exported Win32 clipboard APIs. I admit that I haven't finished that part yet, so there may turn out to be a need for some private hooks, but I'm hoping we can do without.
I think we will at least need some sort of hook in OpenClipboard, so that the driver can poll the host clipboard if it needs to.
The driver will also have to ensure that multiple processes don't compete for clipboard ownership when a non-Wine application holds the host clipboard. It probably has to be done in the explorer process. Otherwise, we'd have lifetime issues as well - any other process might be killed before the clipboard changes.
There are still problems to be solved, but I like the direction this is taking.