I was under the impression that there already was one, but it looks like I was mistaken. I will volunteer to own the Notes *R4* client, which I regularly use. (I suggest having a different owner for Notes R5.)
My employer only recently began providing a VPN access option for Linux, so I've only been back to using Notes with Wine for a few weeks, but it seems to be working very well. The only bug I've noticed is that the left pane of the mail window (in which the "views" are shown) is resized to a zero width when the window is redrawn.