I've been really happy with the performance of my Canon 16-35 with the metabones adapter on my Sony in terms of AF reliability, etc. in some pretty challenging land conditions. I got the adapter on a whim expecting pretty horrible results but it seems to be as functional as on my 5d3 and 1Dx. You say it's possible to use on the Sony, I guess I just need to do a little more in-depth research looking for extension tube compatibility.
If it will work, I might as well go with the Sony 12-24 and just grab another extension tube for the 16-35 w/Metabones and see which I like better.