Love my FA77mm Ltd and would love a high quality modest WA to compliment it... something like a FA25MM F2.0 Ltd Macro would float my boat.
Wouldn't need to be 1 to 1, half life would be more than fine, just ability to close focus and not start noticeable diffraction until f16 or thereabouts.
I'd prolly sell my Irix 15mm and my Tokina 20-35mm, taking a couple of pounds out of my bag. Like others, I don't find a lot of use for 15mm on FF as I thought I would for my style of shooting... Though I prolly wouldn't let go of my manual Soligor 20mm f2.8... it's tiny like a Limited and the bokeh is just too fun. Heck, an updated Limited AF version of the Soligor would be cool for that matter.
Eric